Libyan demonstrators lobbed hand grenades at security forces and set cars ablaze after a rally in Benghazi on Friday in support of a hardline Salafist group which was evicted from the second city.
More than 200 men converged on Benghazi's Al-Jalaa Hospital, which was guarded by members of Ansar al-Sharia until Friday of last week, when anti-militia protesters forced them out, an AFP correspondent reported.
"We want Ansar al-Sharia to come back and protect this hospital," a placard read.
The crowd then marched on a nearby security forces building.
Interior ministry forces fired warning shots in the air from inside the base. Demonstrators responded by throwing hand grenades at the outer walls and torching two parked cars.
Troops arrived quickly on the scene and the crowd dispersed. Some 25 soldiers took up position around the building.
"There is no loss of life -- we have taken control of the situation," General Manaa bin Hamid of the army's newly created National Mobile Force told AFP. He added that the identity of the assailants was unknown.
The rally comes a week after mass demonstrations against militias ended in the eviction of several paramilitary groups from Benghazi, cradle of the 2011 revolt that toppled Moamer Kadhafi.
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Ansar al-Sharia has been accused of but denied involvement in a September 11-12 assault on the US consulate in the city which killed Ambassador Chris Stevens and three other Americans.
A message to US citizens posted on the embassy website on Thursday had warned of plans for demonstrations in both Benghazi and Tripoli.
"Even demonstrations that are meant to be peaceful can become violent and unpredictable. You should avoid them if at all possible," the message said.
In Tripoli, some 200 people marched on Friday against militias and in favour of a unified national army and police, ignoring the warnings of Libya's highest religious authority, Grand Mufti Sadiq al-Geriani.
Geriani, in widely broadcast and published remarks, said this week that people should avoid demonstrations to "prevent bloodshed" given the security vacuum and the risk that these be exploited by "enemies of the revolution."
Violence last Friday killed 11 people in Benghazi.
The upheaval comes as recently appointed Prime Minister Mustafa Abu Shagur, who has pledged to make security a top priority during his tenure, works to put together his cabinet.
The most pressing challenge for the new government is to disband rogue armed groups and discipline brigades that have already put themselves under the authority of the defence or interior ministries.