TRIPOLI: Libya's parliament chief announced in an interview with CBS News on Sunday the arrests of some 50 people over the killing of US ambassador Chris Stevens in an attack he said was planned by foreigners.

US Defence Secretary Leon Panetta said, meanwhile, the American military has no major plans to bolster its forces in the Middle East despite a week of violent protests targeting diplomatic outposts, including at the US consulate in Libya's eastern city of Benghazi in which Stevens died.

“The number reached about 50,” Mohammed al-Megaryef, president of the Libyan National Congress, told CBS.

Stevens and three other Americans were killed on Tuesday when suspected militants fired on the US consulate in Benghazi with rocket-propelled grenades and set it ablaze.

Megaryef said “a few” of those who joined in the attack were foreigners, who had entered Libya “from different directions, some of them definitely from Mali and Algeria.”

”The others are affiliates and maybe sympathisers,” he added.

Megaryef said the government has learned the attack was not the result of a spontaneous outburst of anger over a US-made anti-Islam movie which has triggered sometimes deadly protests in the Arab and Muslim world.

“It was planned, definitely, it was planned by foreigners, by people who entered the country a few months ago. And they were planning this criminal act since their arrival,” he told CBS.

Al-Qaeda in the Arabian Peninsula (AQAP) has said in a statement the attack was in revenge for the killing of the terror network's deputy leader Sheikh Abu Yahya al-Libi in a drone strike in June, and called for more attacks on US targets.

US officials have already deployed counter-terrorism Marine units to Libya and Yemen and stationed two destroyers off the North African coast.

Panetta told reporters before arriving in Tokyo on an Asian tour that with a substantial force already deployed in the region and now boosted by the extra Marine units, the military has the ability to respond as necessary to protect American diplomats.

“We do have a major presence in the region,” he said.

“Having said that we've enhanced that with FAST (Fleet Anti-Terrorism Security Team) teams and others so that if they are requested, they can respond more quickly.”

Sudanese Foreign Minister Ali Karti on Saturday flatly rejected a US request to send special forces to protect the Khartoum embassy, the official SUNA news agency said, quoting his office.

Hours later, US officials announced Washington would evacuate all non-essential staff and family members from Sudan and Tunisia, and warned US citizens against travel to the two countries.