Was U.S. consulate attack an inside job? Investigators probe 'mole' as FBI warns revenge attacks over anti-Muslim Mohammed film could spread to American soil

Investigators looking into possibility that spy aided militants in Tuesday's deadly attack on U.S. consulate in Benghazi
Officials have said attacks are too 'coordinated' to be simple angry mob
Joint Intelligence Bulletin warns violence could hit U.S. and asks religious organisations to guard against attacks
Four killed as protesters march on U.S. Embassy compound in Sana'a, Yemen
Hundreds of protesters angered by an anti-Islam film stormed the U.S. Embassy compound in Yemen's capital and burned the American flag
Smashed windows of the security offices outside the embassy with stones and burned cars before breaking through the main gate of the heavily fortified compound in eastern Sana'a
Sensitive documents have gone missing from compound, including names of Libyans working with Americans
Libyan officials say four men now in custody in relation to attack
Landlord of building says there were 400 rioters and attack could not be prevented

Following the deadly attacks in Libya, investigators are looking into whether a mole gained access to sensitive information, helping Libyan extremists in their deadly attack Tuesday night.

On the 11th anniversary of the September 11 terrorist attacks, militants began firing on the main consulate building, seizing it in only 15 minutes.

A high-ranking Libyan official then insinuated that the spy tipped off the rebels, sending them to the nearby safe house, where two more Americans were killed and one injured in the melee.

Reports have also circulated that the U.S. Department of State knew of the attack up to 48 hours ahead of time, yet chose to do nothing.

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Inside job: Investigators are looking into the possibility that the attack on the U.S. Consulate in Benghazi Tuesday night, pictured, was aided by a spy

Inside job? Officials have said Tuesday's attacks have been 'too coordinated or professional' to be unplanned and could have relied on a mole to give the extremists valuable information

Planned? Officials have said Tuesday's attacks have been 'too coordinated or professional' to be unplanned and could have relied on a mole to give the extremists valuable information

The unnamed official said that a spy could have potentially tipped off invaders on where to find more Americans, the New York Daily News reported.

US Ambassador to Libya Christopher Stevens, who was killed in an attack on the US consulate in Benghazi

Eastern Libya's deputy interior minister, Wanis el-Sharef, said a mob first stormed the consulate Tuesday night and then, hours later, raided a safe house in the compound just as U.S. and Libyan security arrived to evacuate the staff.

That suggested, el-Sharef said, that infiltrators within the security forces may have tipped off the militants to the safe house's location.

The attacks were suspected to have been timed to coincide with the 11th anniversary of the September 11, 2001, terrorist strike in the United States, el-Sharef added, with the militants using the film protest by Libyan civilians to mask their action.

The Independent, citing diplomatic sources, has exclusively reported that the U.S. State Department had known up to 48 hours ahead of the attacks that the compounds in Benghazi and Cairo were potential targets.

However, none of the diplomats in either city were given warning to go on lock-down, the paper reported.

Documents containing delicate information have been lost in the attack, the paper reported. These documents are believed to contain the names of Libyans who are also working for Americans, as well as information on oil contracts.

It is also believed that the attacks could be retribution for a drone strike which killed a top al-Qaeda official in Pakistan, who was said to be Libyan.

Killed in the attack were U.S. Ambassador Chris Stevens, information management officer Sean Smith, and private security guards Glen Doherty and Tyrone S. Woods.

El-Sharef said four people were arrested at their homes Thursday, but he refused to give any further details.

He said it was too early to say if the suspects belonged to a particular group or what their motive was. Libya's new prime minister, Mustafa Abu-Shakour, said authorities were looking for more suspects.

Loss: Sean Smith, 34, an Air Force veteran who had worked as an information management officer for 10 years in diplomatic posts, was also killed

Losses: Private security guards Glen Doherty, left, and Sean Smith, an Air Force veteran who had worked as an information management officer for 10 years in diplomatic posts, was also killed; both were former Navy SEALs

One of five private security guards at the consulate said the surprise attack began around 9:30 p.m. when several grenades that were lobbed over the outer wall exploded in the compound and bullets rained down.

The guard was wounded in the left leg from shrapnel.

He said he was lying on the ground, bleeding and in excruciating pain when a bearded gunman came down the wall and shot him twice in the right leg, screaming: 'You infidel, you are defending infidels!'

'Later, someone asked me who I was. I said I was the gardener and then I passed out. I woke up in hospital,' said the guard, who spoke to The Associated Press from his bed at a Benghazi hospital.

He spoke on condition of anonymity because he feared reprisals and reprimands from his employers.

City in flames: A man stands in front of a vehicle burning at the U.S. embassy in Sana'a after demonstrators attacked the U.S. Embassies in Yemen on Thursday in protest at a film they consider blasphemous to Islam

Pain: A protestor grimaces after he's shot with tear gas fired by riot police, unseen, near the U.S. Embassy in Sanaa, Yemen

Fury: Chanting 'death to America,' hundreds of protesters angered by an anti-Islam film stormed the U.S. Embassy compound in Yemen's capital and burned the American flag. It was the latest in a series of attacks on American diplomatic missions in the Middle East

Fervent belief: Protesters climb a fence surrounding the U.S. embassy in Sana'a as they fight to discredit the 'blasphemous' film

The witness account came as protests of the mysterious film, Innocence of Muslims, continued in the Middle East.

An angry throng broke into the U.S. Embassy in Yemen, and clashes between security forces and demonstrators near the fortress-like embassy compound in the heart of Cairo left nearly 200 people injured and two police trucks burned.

Speaking at his Benghazi office, el-Sharef, who was running the Interior Ministry's operations room commanding security forces in the city during the attack, gave the most detailed account to date to come out of Libya of what happened the night of the attack. His version, however, leaves some questions unanswered and does not provide a definitive explanation on the motives behind the attack and the identity of the perpetrators.

Meanwhile, top officials warned Thursday that the violence which has engulfed the Middle East following the release of a film mocking the Prophet Mohammed could spread to the U.S.

The Joint Intelligence Bulletin suggested that as well as widespread protests, the furore could be used by extremists to radicalise American Muslims.

The report, issued by the FBI and the Department of Homeland Security, follows three days of angry demonstrations in Muslim countries directed at U.S. embassies, which led to the killing of the American ambassador to Libya on Tuesday night.

The report warned that 'the risk of violence could increase both at home and abroad as the film continues to gain attention', according to ABC News.

It continued: 'First responders should remain aware of the potential for spontaneous large crowds and protests that could overwhelm resources and should be vigilant for possible efforts to encourage peaceful protesters to commit acts of violence.'

Fury: Muslim men in Bangladesh burned an American flag during protests against an anti-Mohammed film on Thursday

Clash: Fights between protesters and riot police left burnt-out vehicles near the American embassy in Cairo

Defiant: A demonstrator throws a stone at police in Cairo, near the American embassy and iconic Tahrir Square

Tear gas: Egyptian authorities went to great length to calm down protesters and end the threat to the U.S. embassy

Defence: Riot police shout warnings to protesters as they guard the road leading to the embassy on Thursday

Officials were particularly cautious about the risk of Islamic radicals exploiting the outrage over the film to engineer attacks against mainstream society and other faiths.

They suggested that 'violent extremist groups in the United States could exploit anger over the film to advance their recruitment efforts', and asked religious bodies to prevent 'plotting against Jewish, Coptic, Islamic, or any other faith-based communities'.

The bulletin comes as the rising anger provoked by the film has seen protestors storm U.S. embassies in Muslim countries from Egypt to Yemen, where four people have been killed and dozens others injured.

Chanting 'death to America', hundreds of protestors marched on the U.S. Embassy compound in Yemen's capital today, where they burned the American flag, used stones to smash windows, and set fire to cars, before breaking through the main gate of the heavily fortified compound in eastern Sana'a.

Security has been ramped up at U.S. embassies and consulates around the world, and at least one cemetery for American veterans, while President Obama called the leaders of Libya and Egypt to continue helping him to ensure the safety of diplomatic personnel.

Chaos: Yemeni protestors break a door of the U.S. Embassy with a pole after ripping off the metal plaque

Fragile defences: Dozens of protesters smash the building's windows to show their anger at the film's perceived Islamophobic message

Attack: Yemeni protesters storm the US embassy during a protest. Yemen's embassy in Washington said no casualties were reported

Attack: Yemeni protesters storm the U.S. embassy during a protest today. Yemen's embassy in Washington said no casualties were reported

Blazing fire: Yemeni forces drive back the protesters as they approached the main gate of the mission

Breaking in: Demonstrators break a widow of the U.S. Embassy - tyres blazed outside the compound and protesters scaled the walls

Heavy smoke rises from the U.S. Embassy compound in Sana'a, Yemen, amid angry clashes between protestors and riot police

One of those killed in Benghazi alongside U.S. Ambassador Christopher Stevens was 42-year-old Glen Doherty, a family friend told CBS Boston today.

Libyan authorities have made four arrests in the investigation into the attack on the U.S. consulate in Benghazi in which the U.S. ambassador and three embassy staff were killed, the deputy interior minister said on Thursday.

'Four men are in custody and we are interrogating them because they are suspected of helping instigate the events at the U.S. consulate,' Wanis Sharif told Reuters.

He gave no more details.

There were protests in Tunisia, Sudan and Morocco overnight, and the demonstrations have reached Cairo and Baghdad.

Medical attention: A Yemeni man takes a protester to the hospital after sustaining injuries during clashes with riot police outside the U.S. embassy in Sana'a on Thursday

Bloody: A blood-soaked protester shouts slogans after sustaining injuries from a confrontation with riot police who fired tear gas at them outside the embassy

Climbiing: Yemeni demonstrators scale the front gate of the U.S. embassy in Sana'a after the Muslim nation became the latest to be marred by street protests over a film ridiculing the prophet Mohammed

On Thursday, riot police in Indonesia were standing guard outside the U.S. Ambassador's Jakarta residence in anticipation of further action.

Once inside the compound in Sana'a, Yemeni protestors brought down the U.S. flag, burned it and replaced it with a black banner bearing Islam's declaration of faith - 'There is no God but Allah.'

CNN reported that four people were killed in the clashes, and dozens of other security officials and protesters were injured.

Before storming the grounds, demonstrators removed the embassy's sign on the outer wall, set tires ablaze and pelted the compound with rocks.

Yemeni security forces who rushed to the scene fired in the air and used tear gas to disperse the demonstrators and were eventually able to drive them out of the compound. It was not immediately clear whether anyone was inside the embassy at the time of the attack.

Emergency aid: Yemeni medics take an injured protester on a motorcycle to the hospital

Streets of chaos: Protesters throw stones at riot police near the U.S. embassy in Sana'a after riots spread into the streets

Marching: Yemeni men shout slogans during a protest

Dangerous: Heavy smokes rises from the U.S. embassy in Sana'a as Yemeni protesters try to break the security camera at the compound

Fighting with fire: Protesters burn tyres - the violence has raised worries that further protests could break out around the Muslim world as anger spreads over the film

Written on stone: A graffiti artist writes 'Muhammad is the Messenger of Allah!' on a wall

Some protestors held aloft banners declaring 'Allah is Greatest'. Tires blazed outside the compound and protesters scaled the walls.

'We can see a fire inside the compound and security forces are firing in the air. The demonstrators are fleeing and then charging back,' one witness said.

It was similar to an attack on the US Embassy in the Egyptian capital of Cairo on Tuesday night.

Witnesses said there were some injuries on both sides but gave no exact figures.

Yemen, a key U.S. ally, is home of al Qaeda in the Arabian Peninsula (AQAP), which is viewed by Washington as the most dangerous branch of the militant network established by Osama bin Laden.

Yemen is fighting an al Qaeda-backed insurrection largely in the south of the country. Its embassy in Washington did not report any casualties.

An embassy statement said Yemen's government condemned the attack by protesters angry at a film seen as insulting to Islam, adding security forces had restored order at the complex.

Relationship: Yemen, a key U.S. ally, is home of Al Qaeda in the Arabian Peninsula (AQAP), which is viewed by Washington as the most dangerous branch of the militant network established by Osama bin Laden

Demonstrations: A Yemeni protestor, left, holds a white flag with Islamic inscription in Arabic that reads, 'No God but Allah, and Mohammed is his prophet,' in front of the U.S. embassy

Mass fury: A Yemeni protester waves the flag as thousands of people gather at the main gate of the mission

Clashing sides: The furious activists storming the embassy in the Yemeni capital were fired at by security forces, according to local media reports

Protection: Protesters climb a fence as security guards tried to hold them off by firing into the air

Dramatic: The demonstrators try to break into the embassy by tearing up the roof and pounding it with makeshift weapons

Trampled underfoot: While some youths raise Islamist flags, left, others walk on U.S. and Israeli national flags

Refuted: An embassy statement said Yemen's government condemned the attack by protesters

Angry: A protestors smashes a window and picks through the glass in an attempt to enter a building in the embassy

TIMELINE OF TERROR: WHAT AUTHORITIES BELIEVE HAPPENED DURING THE LATE-NIGHT CONSULATE RAID

Well-armed Libyan extremists launched a sustained attack on the U.S. Consulate in Benghazi, Libya, on Tuesday, killing four State Department employees, including the American ambassador to Libya Chris Stevens and foreign service officer Sean Smith, and wounding three others.

The consulate, like all other U.S. diplomatic missions around the world, conducted a pre-9/11 anniversary security check. It found no imminent threat and therefore no need to boost security around the anniversary, according to senior U.S. officials, who spoke on condition of anonymity because the reporting of the incident is still preliminary.

The consulate consists of a main building and a nearby annex, each of which are protected by local Libyan guard force, a physical perimeter barrier and a ‘robust’ American security presence inside the compounds. All times are local Benghazi time, and accounts are from officials

10:00pm Tuesday - The main consulate building begins began taking fire from unknown Libyan extremists. There are about 25 to 30 employees in the consulate and the annex at the time of the attack.

10:15 pm - Attackers gain access to main consulate building and set compound on fire. In the ensuring chaos, many escape the building, but Stevens, Smith and a regional security officer remain inside. They become separated due to heavy smoke and confusion while trying to evacuate. The security officer makes it outside and he and others from the consulate and annex go back into the building to try to rescue Stevens and Smith. They find Smith dead and pull him out but are forced by the flames, smoke and gunfire to withdraw before they can locate Stevens.

10:45pm - A group of security officers from the annex try to take the consulate building back from the attackers, but they are repelled. Everyone rescued is brought to the annex.

Midnight - The annex comes under heavy fire from the attackers. The shooting lasts more than two hours during which the other two Americans are killed and two Americans are wounded.

2:30an Wednesday - Libyan and U.S. security forces retake the annex. Officials believe that Stevens got out or was pulled out of the main consulate building during the battle for the annex and was taken to the hospital. The officials do not know if Stevens was alive when he arrived at the hospital.

6:00am - U.S. officials are told that Stevens is dead but are not able to confirm it immediately because they have not seen the body. The body is returned to U.S. personnel at the Benghazi airport at dawn.