Islamist militias in Libya have lost two major areas in the eastern city of Benghazi, military sources and residents have told the BBC.
“People are celebrating on the streets,” a resident said.
Fighters loyal to anti-Islamist Gen Khalifa Haftar are reported to have taken over the port, a hospital and have cut off a key weapons supply line.
Thousands have fled more than a year of fighting in Benghazi, the birthplace of the 2011 uprising.
Once in the Libyan army, Gen Haftar fought with revolutionaries to overthrow long-time leader Muammar Gaddafi.
Libya has since fragmented and has rival parliaments backed by various militias and brigades spawned by the uprising.
BBC North Africa correspondent Rana Jawad says the chaos has allowed Islamic State fighters to gain a foothold in the country, and some are believed to be fighting with other Islamist militias in Benghazi.
In January, the UN brokered a deal between rival lawmakers to form a unity government, but this has not yet happened.
The latest military gains will give Gen Haftar a stronger hand in Libya’s volatile political landscape, and it is not yet clear if he is giving his backing to the unity agreement, our correspondent says.
Last year, he was appointed as the head of armed forces for the parliament based in the eastern port city of Tobruk.
Some of the Islamist militias he has been battling in his hometown of Benghazi are backed by political factions in the west, where the Tripoli administration is based.