Libya's interim president, Mohammed Magarief, suggested today that al-Qaeda was behind the deadly assault on the US consulate in Benghazi, which claimed the life of the US ambassador.

"I won't be surprised to discover that they were the planners of this sinister attack on American consulate, particularly when we think of, or we consider they are choosing the 11th of September as the date for carrying out this operation," he said.

Mr Magarief said that the second part of the attack, on a safe house used by consulate workers, shows the assault was planned in advance.

"All this indicates clearly that the attackers are well trained and well prepared and have planned this in advance," he said.

His comments contrast with the US view today, which suggests that Tuesday's attack was not a premeditated assault tied to the anniversary of 11 September.

The US ambassador to the United Nations said today that the assault, which also killed three other Americans, was a spontaneous reaction to an anti-Muslim video.

Susan Rice said that evidence gathered by a White House investigation into the attacks so far shows no indications of a premeditated or coordinated strike.

She said the deadly protest in Benghazi appeared to be a copycat of demonstrations that had erupted hours earlier outside the US Embassy in Cairo, spurred by excerpts from a film posted on YouTube mocking the Prophet Muhammad.

Mr Magarief said today that the investigation into the attacks was ongoing and that a number of arrests had been made.

He said the Libyan authorities would cooperate fully with the US government in its investigation.

"The Americans being the target of this attack, I think it's our duty, it's our responsibility to invite them to help us in carrying out the investigation," he said.

Embassies on alert as anger persists

Western embassies across the Muslim world remained on high alert today and the US urged vigilance after days of anti-US violence provoked by the video, seen as insulting to the Prophet Muhammad.

With protests against the film continuing from London to Lahore, Western diplomatic missions were on edge.

Germany followed the US lead and withdrew some staff from its embassy in Sudan, which was stormed on Friday.

The US ordered non-essential staff and family members to leave its embassy yesterday after the Sudanese government turned down a US request to send Marines to bolster security.

Non-essential US personnel have also been withdrawn from Tunisia, and the US urged its citizens to leave the capital Tunis after the embassy there was targeted on Friday.