The US State Department has urged American citizens to leave the Tunisian capital Tunis and warned its citizens of the risks of travelling to Sudan following anti-American protests there.

"The Department of State ordered the departure of all non-emergency US government personnel from Tunisia, following the attack on the US Embassy in Tunis," the department said in a statement.

"The airport in Tunis is open and US citizens are encouraged to depart by commercial air."

The State Department also urged US citizens to avoid travel to Darfur, the Blue Nile and Southern Kordofan regions of Sudan.

Sudan earlier rejected a US request to send a platoon of Marines to bolster security at the US embassy.

Yesterday, around 5,000 people protested against a film that insults the Prophet Muhammad, storming the German embassy before breaking into the US mission.

They also attacked the British embassy. At least two people were killed in clashes with police, according to state media.

A US official said yesterday that the US would send Marines to Sudan to improve security at the embassy, which is located outside Khartoum for security reasons.

But Sudanese Foreign Minister Ali Ahmed Karti told the state news agency SUNA: "Sudan is able to protect the diplomatic missions in Khartoum and the state is committed to protecting its guests in the diplomatic corps."

In Egypt, riot police stormed into Cairo's Tahrir Square and rounded up hundreds of protesters early this morning after four days of clashes sparked by the film.

Security forces secured the square, just a few hundred metres from the US embassy, and formed cordons in the surrounding roads.

Plain-clothes officers patrolled the area, grabbing anyone they saw as suspicious. There was no sign of protests by mid-morning and traffic through Tahrir resumed.

The protesters said they wanted to expel the US ambassador to punish the US over the film which was produced in California.

US Defence Secretary Leon Panetta called on Egypt's government yesterday to ensure the embassy's safety.

Afghanistan's Taliban has claimed responsibility for an attack on a base which US officials said killed two US Marines, saying it was in response to the controversial film.

Camp Bastion, in the southern Helmand province, came under mortar, rocket-propelled grenade and small arms fire late yesterday in an attack in which several servicemen were wounded.

"The aim of this attack was revenge against Americans for the anti-Prophet movie," said Taliban spokesman Qari Yousuf.

Earlier this week, the Afghan Taliban said they were doing everything in their power to either kill or kidnap Queen Elizabeth's grandson in what they dubbed their "Harry Operations."

Man questioned in California over film

A California man linked to the anti-Islam film that sparked the violent protests across the Muslim world was taken in for questioning today by authorities investigating possible violations of his probation for a bank fraud conviction.

Nakoula Basseley Nakoula, 55, voluntarily left his home in the early hours of this morning for a meeting at a sheriff's station in the Los Angeles suburb of Cerritos, said Steve Whitmore, a spokesman for the Los Angeles County Sheriff's Department.

"He will be interviewed by federal probation officers," Mr Whitmore said, adding that Mr Nakoula had not been arrested but would not be returning home immediately.

"He was never put in handcuffs ... It was all voluntary."

Mr Nakoula was ushered out of his home and into a waiting car by sheriff's deputies, his face shielded by a scarf, hat and sunglasses.

He has denied involvement in the incendiary low-budget film in a phone call to his Coptic Christian bishop.