U.S.-backed fighters in Syria converged from three sides on an Islamic State stronghold near the Turkish border Thursday, June 9, while Iraqi special forces pushed deeper into Fallujah, one of the last bastions of the militant group in western Iraq, the Associated Press reports.

In Libya, IS militants were fleeing their stronghold of Sirte as forces loyal to a U.N.-brokered government advanced, with some fighters reportedly cutting off beards and long hair to blend in with civilians.

The anti-IS offensives posed a significant challenge to the extremist group as it tries to stave off multiple attacks across parts of Syria and Iraq, where it declared a so-called caliphate in 2014, and in more recently seized territory in chaotic Libya.

If the U.S.-backed Syria Democratic Forces capture Manbij, it will be the biggest strategic defeat for IS in Syria since July 2015, when it lost the border town of Tal Abyad, a major supply route to the militants' de facto capital of Raqqa, AP says.

Manbij, which had a prewar population of 100,000, is one of the largest IS-held urban areas in northern Aleppo province and is a waypoint on an IS supply line between Raqqa and the Turkish frontier.

In a sign of the town's perceived significance, the SDF's advances were accompanied by intense airstrikes from the U.S.-led coalition battling the IS militants. The U.S. Central Command said the coalition has conducted more than 105 strikes in support of the battle to liberate Manbij.

The airstrikes recalled the battle for the Kurdish town of Kobani in northern Syria. That campaign saw hundreds of U.S. airstrikes to support Kurdish forces who wrested Kobani from IS in January 2015 after four months of fighting that left the town in ruins.

Since then, members of the U.S. and French military have joined in to advise the anti-IS forces in northern Syria.