Heavy fighting broke out between Libya's army and a militia in the port city of Benghazi in the country's volatile east on Friday, residents said.
Gunfire and explosions were heard for more than one hour in the early hours. The army's special forces moved vehicles to the scene of fighting near the city's security headquarters, residents said.
The identity of the enemy was not immediately clear, residents said, though there have been frequent clashes in the city between security forces and Islamists militants, Reuters reported.
There were reports of casualties but government and security officials could not be immediately reached for comment.
The fighting came days after a suicide bomber had detonated an explosive-packed minibus outside a Libyan army camp in Benghazi, killing two people and wounding two more in the second suicide attack since December.
Car bombings and assassinations of soldiers and police are common in the eastern city, where troops have clashed regularly with militants from Islamist group Ansar al-Sharia - listed as a terrorist organization by Washington.
Most countries have closed their consulates in Benghazi and some foreign airlines have stopped flying there since the U.S. ambassador and three other Americans were killed in an Islamist militant attack in September 2012.
Libya's central government is struggling to control armed groups, militias and brigades of former rebels who helped oust Gaddafi in 2011 and now refuse to disarm.