Libyan forces said Friday that they have retaken control of the port in Islamic State group's stronghold of Sirte after fierce fighting. The forces, aligned to Libya's U.N.-backed Government of National Accord (GNA), which arrived in Tripoli in March, began the battle to retake the city last month.

Earlier this week, airstrikes were conducted over ISIS positions in Sirte while naval forces fired missiles into the port, which was controlled by the militant group, officials reportedly said, adding that the offensive continues.

General Muhammad al-Ghusri, a spokesman for the forces, reportedly said that the senior ISIS leaders fled into the desert to the south following the attack, but many militants were still under siege in the city center.

The clashes between Libyan forces and ISIS militants centered on the Ougadougou conference center, which was once a venue for international summits but has now become an ISIS command center, BBC reported. The center was reportedly targeted by government forces with heavy artillery fire, backed by warplanes.

More than 100 fighters from the GNA-backed forces have been killed and more than 500 others injured since the assault to recapture Sirte began in early May.

Two thirds of Sirte’s 80,000-strong population have fled since ISIS seized the city. The group, which controls swaths of territory across the Mediterranean Sea in Iraq and Syria, gained a foothold in Libya amid chaos that consumed the North African nation since the fall of its longtime dictator Moammar Gadhafi in 2011.