Libya's interior minister has sacked Benghazi security chiefs after last week's deadly attack on the US consulate in the eastern city, according to official statements seen Monday by AFP.

Deputy interior minister for the eastern region, Wanis al-Sharef, and the head of national security for Benghazi, Hussein Bou Hmida, were both replaced, said two separate statements dated September 12, a day after the attack.

Ambassador Chris Stevens and three other Americans were killed as the Benghazi consulate came under fire from rocket-propelled grenades during a protest against an anti-Islam film made in America.

General Bou Hmida would be replaced by Colonel Salaheddin Doghman who would also temporarily fill in for Sharef until his successor is found, according to the texts signed by Interior Minister Fawzi Abdelali.

Libya announced on Sunday the arrest of 50 suspects over the killing of the Americans, and has blamed the Benghazi attack on foreign extremists.

A low-budget trailer for the film entitled "Innocence of Muslims," believed to have been produced by a small group of extremist Christians in the United States, has sparked furious anti-American protests across the Islamic world.

The first protests erupted in Cairo, where demonstrators stormed the US embassy on Tuesday night, replacing the Stars and Stripes with an Islamic banner.

Hours later, the US consulate in Benghazi was attacked.

Announcing the 50 arrests, Libya's parliament chief on Sunday blamed the attack on a few foreign extremists who he said entered the country from Mali and Algeria and pre-planned it with local "affiliates and sympathisers."

"It was planned, definitely, it was planned by foreigners, by people who entered the country a few months ago," Mohammed al-Megaryef, president of the Libyan National Congress, told US broadcaster CBS.

Ambassador Stevens is believed to have died from smoke inhalation after becoming trapped in the blazing diplomatic compound as it came under fire from RPGs, mortars and small arms for several hours.

Since the consulate attack, the United States has deployed counterterrorism Marine units to Libya to protect the Tripoli embassy and stationed two destroyers off the North African coast.

Anti-US protests have shaken a large swathe of Muslim countries in Africa, Asia and the Middle East, and many of the protests have been deadly.