Hundreds of Libyans held a demonstration in Tripoli on Friday demanding the breakup of militia groups and the formation of a national army and police.

The protesters gathered at Martyrs Square at the heart of the capital, despite warnings and religious edicts by the country's top cleric against the demonstrations and after similar protests in Benghazi turned violent last week when crowds stormed the headquarters of militia groups and clashed with militiamen.

Security forces were on high alert, diverting traffic away from the square and running checkpoints on main roads. Protesters carried signs that read: "Libya is in a trap, there is no army or police." They also chanted: "Where is the Libyan national army?"

After last year's killing of Libya's longtime dictator Moammar Gadhafi and the collapse of his regime, the country suffered a deep security vacuum which was quickly filled by local militia groups formed initially of rebel forces that fought Gadhafi's forces in an eight-month rebellion.

However, over the months, the militias mushroomed in number and their ranks swelled with youths ready to take the law into their own hands, gradually earning them a bad reputation on the street.

The killing of the U.S. ambassador to Libya, Chris Stevens, along with three other Americans in an attack on the U.S. consulate in the eastern city of Benghazi, capped Libyans' discontent with the armed groups and boosted demands for a unified national army and police.

On Thursday, U.S. Defence Secretary Leon Panetta said there was no doubt that extremists had planned and carried out the consulate attack. "It was a terrorist attack," Panetta said when asked at a Pentagon news conference whether al-Qaida was involved, adding that investigators had yet to determine which group was implicated.

Investigations into the attack have been marred by the inability of FBI agents — sent to Libya last week — to enter Benghazi for security concerns, according to two law enforcement officials who said the city must be made secure before the FBI sends investigators there. The officials demanded anonymity because they are not authorized to speak on the record about an ongoing investigation.

FBI 'moving forward' on investigation

At FBI headquarters Friday, spokesman Paul Bresson said "we are moving forward with our investigation," but he declined to comment on the specific location of the agents.

Separately, the State Department is further reducing the U.S. Embassy staff in Tripoli for security reasons. The embassy warned Americans of possible demonstrations in the capital and Benghazi on Friday.

Libyan leaders have vowed to disband the "illegitimate" militias while recognizing other pro-government groups. On Sunday, the Libyan army said it carried out raids on several militia outposts operating outside government control in the capital, while in the east, the militia suspected in the Sept. 11 attack on the U.S. Consulate said it had disbanded on orders of the country's president.

President Mohammed el-Megarif said on Thursday that his government has disbanded about 10 militia groups and will continue to take action against Muslim extremists. He described the attack on the U.S. consulate as the final straw. He was speaking in New York.

Authorities formed a new "instant intervention force" to disband the militias and assume control over assets previously held by them, but many Libyans oppose granting legitimacy to other pro-government groups and demand authorities to integrate them into the national army or police as individuals, not blocs.

'The Friday for Tripoli Rescue'

Hours before Tripoli protests, dubbed "The Friday for Tripoli Rescue," Muslim clerics urged in their weekly sermons for worshippers to refrain from joining them, in order to avoid bloodshed. Grand Mufti al-Sadek al-Gharyani issued a fatwa calling on people in Tripoli, Benghazi and other cities not to participate, urging "obedience."

The country's newly elected Prime Minister Mustafa Abushagur repeated the same warnings in a news conference aired Thursday on national TV, saying, "we don't want to lose more souls or spill more blood." Libya's chief of staff, Gen. Youssef al-Mangous, retreated pledges to disband militias that resist state authority.

In Tripoli, former rebel forces from different cities which last year drove Gadhafi from his seat of power have remained, such as the Misrata militia Saadoun al-Sewhli. Some have turned over their offices voluntarily to the government, while others were forced to do so. Among the most powerful militias in Tripoli is one group called al-Qaaqaa, and another called Bashir al-Saadawi. Most of the groups there are pro-government and considered legitimate by the country's leaders.