Eight people were killed and 15 wounded when fighting broke out on Monday between the Libyan army and Islamist militants in the eastern city of Benghazi, medical sources said.
Libya is in protracted turmoil three years after the NATO-backed war that ousted Muammar Gaddafi, with Islamist, anti-Islamist, regional and political factions locked in conflict.
The Ansar al-Sharia militant group attacked a camp on Monday belonging to army special forces, residents there said. Forces of a renegade general fighting Islamists later joined the battle, using combat helicopters, they added.
Among the eight dead were at least five soldiers, according to a hospital who asked not to be identified.
Irregular forces loyal to former army general Khalifa Haftar - who wants to purge the North African state of Islamist militants he says the weak central government has failed to control - supported the army as fighting spread to other parts of Benghazi, his spokesman Mohamed al-Hejazi said.
Helicopters took off from Benghazi's Benina air base, where regular military units have joined Haftar's campaign which began last month, residents said.
The government, rival militia brigades and political factions have rejected Haftar's offensive against militants as an attempted coup, after his forces also stormed parliament a week ago.
Ansar al-Sharia, listed as a terrorist group by Washington, warned the United States last week against interfering in Libya's crisis and accused Washington of backing Haftar.
Gaddafi's one-man rule, followed by three years of unrest, have left Libya with few functioning institutions and no real national army to impose authority on the competing militias and brigades of former rebels who have become power-brokers.
The acting prime minister, Abdullah Al-Thinni, refused on Wednesday to hand over power to a newly elected premier. The OPEC oil producer now has two prime ministers and a parliament deadlocked by splits between factions.
REUTERS