Protests against the film, frequently held on Fridays, have spread across the Muslim world.
 

A statement on the website of the US embassy in Tripoli warned that demonstrations were possible in both the capital and Benghazi on Friday.
 

"This is a temporary further drawdown of staff for security reasons," a state department official said in New York.
 

"We will review our posture again early next week with the goal of restoring staff as soon as conditions allow."
 

It was not revealed how many staff were being withdrawn from Tripoli.

Christopher Stevens and three other Americans were killed during the Benghazi attack, which targeted the US consulate in the city on 11 September.
 

Stevens died of smoke inhalation when he was trapped alone inside the burning consulate after it was set upon by militants.
 

Another diplomat, Sean Smith, and two US security men were also killed.
 

"It was a terrorist attack," Defence Secretary Leon Panetta said on Thursday.
 

"As we determined the details of what took place there and how that attack took place, [...] it became clear that there were terrorists who had planned that attack, and that's when I came to that conclusion," he explained.
 

His comments came a day after Secretary of State Hillary Clinton seemed to link the Benghazi attack to militants with ties to al-Qaeda in the Islamic Maghreb.
 

However, Mr Panetta said investigations into which group was behind the attack were still continuing.
 

Libyan Prime Minister-elect Mustafa Abushagur has said that an investigation is under way but officials do not yet have a definite idea of which group was responsible for the deaths.