America 'was warned of embassy attack but did nothing': State Dept 'had credible information 48 hours before'

The killings of the US ambassador to Libya and three of his staff were likely to have been the result of a serious and continuing security breach, The Independent can reveal.

American officials believe the attack was planned, but Chris Stevens had been back in the country only a short while and the details of his visit to Benghazi, where he and his staff died, were meant to be confidential.

The US administration is now facing a crisis in Libya. Sensitive documents have gone missing from the consulate in Benghazi and the supposedly secret location of the "safe house" in the city, where the staff had retreated, came under sustained mortar attack. Other such refuges across the country are no longer deemed "safe".

Some of the missing papers from the consulate are said to list names of Libyans who are working with Americans, putting them potentially at risk from extremist groups, while some of the other documents are said to relate to oil contracts.

According to senior diplomatic sources, the US State Department had credible information 48 hours before mobs charged the consulate in Benghazi, and the embassy in Cairo, that American missions may be targeted, but no warnings were given for diplomats to go on high alert and "lockdown", under which movement is severely restricted.

Mr Stevens had been on a visit to Germany, Austria and Sweden and had just returned to Libya when the Benghazi trip took place with the US embassy's security staff deciding that the trip could be undertaken safely.

Eight Americans, some from the military, were wounded in the attack which claimed the lives of Mr Stevens, Sean Smith, an information officer, and two US Marines. All staff from Benghazi have now been moved to the capital, Tripoli, and those whose work is deemed to be non-essential may be flown out of Libya.

In the meantime a Marine Corps FAST Anti-Terrorism Reaction Team has already arrived in the country from a base in Spain and other personnel are believed to be on the way. Additional units have been put on standby to move to other states where their presence may be needed in the outbreak of anti-American fury triggered by publicity about a film which demeaned the Prophet Mohamed.

A mob of several hundred stormed the US embassy in the Yemeni capital Sanaa yesterday. Other missions which have been put on special alert include almost all those in the Middle East, as well as in Pakistan, Afghanistan, Armenia, Burundi and Zambia.

Senior officials are increasingly convinced, however, that the ferocious nature of the Benghazi attack, in which rocket-propelled grenades were used, indicated it was not the result of spontaneous anger due to the video, called Innocence of Muslims. Patrick Kennedy, Under-Secretary at the State Department, said he was convinced the assault was planned due to its extensive nature and the proliferation of weapons.

There is growing belief that the attack was in revenge for the killing in a drone strike in Pakistan of Mohammed Hassan Qaed, an al-Qa'ida operative who was, as his nom-de-guerre Abu Yahya al-Libi suggests, from Libya, and timed for the anniversary of the 11 September attacks.

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