Army officers have been appointed to take over two powerful militias in the eastern Libyan city of Benghazi, after the president ordered that all militias join the armed forces or disband.

The move reflects increasing pressure on the government to control or disband the country's militias, many of which it had relied upon for securing Libya in the turmoil following last year's ouster of Muammar Gaddafi.

The military also took over at least one compound being used by the armed groups in Benghazi.

The city's brigades have been blamed for violence that led to the death of Chris Stevens, the US ambassador in Benghazi, on September 11.

Colonel Ali al-Sheikhi, the spokesman for Libya's joint chiefs of staff, told the news agency LANA on Monday that the chiefs of the Rafallah Sahati Brigade and the Feb 17 Brigade, two groups that authorities had allowed to manage security in the eastern city of Benghazi, would be replaced with army commanders.

Meanwhile, fighters calling for more recognition briefly exchanged fire outside the national congress in Tripoli on Tuesday, members of the national assembly said.

"They started fighting among each other, first just hitting each other and then exchanging fire," congress member Nizar Kawan said, adding that some protesters were carrying banners saying "do not sideline the revolutionaries".

"Some of them were saying they should end the protest, others did want to and it escalated."

Anger at militias

A second congress member, who declined to be named, said that politicians were evacuated to a nearby hotel.

"Security forces asked congress members to leave the building," he said.

"Security forces closed off the area and started shooting in the air to stop the protesters."

Anger at the militias boiled over following the killing of the top American diplomat in Libya and three US mission staffers in an assault on the consulate in Benghazi on Sept. 11.

The attack followed an angry protest against an anti-Islam film produced in the US which has riled many in the Muslim world.

Members of the armed group Ansar al-Shariah militia are suspected of being behind the attack.

Many of Libya's militias were formed in the eight-month war against Gaddafi, but more groups sprang up after the end of fighting in October.

With the country trying to rebuild after 42 years of Gaddafi, the groups paid little attention to successive interim leaders.

They were accused of bullying citizens, operating independent prisons and holding summary trials for Gaddafi loyalists.

Recently, Salafi-led militias have also attacked shrines, such as tombs associated with religious figures, that they considered to be counter to their strict view of Islam.