Despite more than three weeks of airstrikes by the United States-led coalition in the region, militants of the Islamic State group have continued to advance deeper into the Syrian border town of Kobani, the Syrian Observatory for Human Rights said late on Monday, according to an Al Jazeera report. The militant group now controls nearly half the town.

The Islamic State group carried out at least six suicide bombings near the center of the town on Monday, killing an unknown number of people, according to media reports. Twenty-six ISIS militants were also killed in clashes with Kurdish forces, Anadolu Agency reported, citing sources on the ground.

Fierce clashes between ISIS militants and Kurdish fighters were reported less than a mile from the Turkish border, the Observatory said, adding that the Islamic State group had seized major buildings in the city center late on Monday.

U.S.-led coalition warplanes also carried out at least three airstrikes, targeting the Islamic State group’s strongholds in the south and northeast of the town on Monday, the Observatory reported.

If ISIS seizes control of the town’s border crossing with Turkey, it could cut off all access to the town, where thousands of civilians, mostly Kurds, are still believed to be trapped. The United Nations had earlier warned that these civilians “will most likely be massacred” if the town falls.