The Islamic State’s (ISIS/ISIL) grip over the Libyan city of Sirte, which was once considered the jihadist group’s largest stronghold outside Iraq and Syria, has been reduced to three neighborhoods, according to the Pentagon.

That assessment comes nearly four months after the top U.S. commander in the region estimated that the number of ISIS fighters in Libya had nearly doubled to between 4,000 and 6,000.

Sirte has been declared fully surrounded and nearly liberated on separate occasions over nearly the last three months, but fighting has continued into September.

Earlier this week, Reuters reported, “Libyan forces said they captured a residential neighborhood in central Sirte from Islamic State on Monday, leaving just one district of the city still occupied by the militants.”

During a press briefing Thursday, U.S. Navy Capt. Jeff Davis, a Pentagon spokesman, indicated “Islamic State forces have been reduced to just three neighborhoods in Sirte…as the U.S. extended its air campaign over the city for up to another 30 days,” reports Voice of America (VOA).

“They’re literally with their backs against the ocean at this point,” Davis told reporters.

Fighters loyal to the United Nations-backed Government of National Accord (GNA) in Libya launched an offensive in mid-May with the assistance of the United States and other Western nations to push the Islamic State, also known as IS, out of the city.

VOA reports that the U.S. military began launching airstrikes in support of the offensive on August 1.

“These strikes — 108 in total as of Thursday — have aided forces aligned with the U.N.-backed government in Libya as they push IS out of the city,” points out the news agency.

Unlike airstrikes targeting ISIS in its so-called caliphate in Syria and Iraq, “each and every one of those strikes” was launched at the behest of the GNA, noted the Pentagon spokesman.

The U.S. military had been authorized to launch strikes over Sirte until the end of August. However, VOA learned from an anonymous defense official that the authority had been extended into September.

Another unnamed American official told VOA that “two U.S. Navy warships, the USS Wasp and the USS Carney, will remain off the coast of Libya to continue striking IS targets.”

Nearly the middle of last month, ISIS admitted that it controlled four neighborhoods in Sirte. In a desperate act to maintain control of the city, ISIS launched a wave of suicide attacks around that time.