Kurdish fighters captured six buildings used by Islamic State fighters besieging the Syrian town of Kobani on Tuesday, and seized a large amount of the militant group’s weapons and ammunition, a group monitoring the war said, according to Reuters.

Islamic State has been trying to take control of the town, also known as Ayn al-Arab, for more than a month in an assault that has driven tens of thousands of Kurdish civilians over the border into Turkey and drawn strikes by U.S.-led forces.

The hardline Sunni Muslim group, an offshoot of al Qaeda, has captured large areas of Iraq and other parts of Syria and declared an Islamic caliphate.

Kurdish fighters seized six buildings used by Islamic State on the edge of the town and took rocket-propelled grenade launchers, guns and machine gun ammunition, the Britain-based Syrian Observatory for Human Rights said.

The clashes killed around 13 Islamic State militants, including two senior fighters, according to the Observatory which tracks the conflict using sources on the ground.

Kurdish forces appear to have made other gains in recent days of fighting. Last week they blocked a road Islamic State was using to resupply their forces, the first major gain against the jihadists after weeks of violence.

“During the last few days we have made big progress in the east and southeast,” said Idris Nassan, an official in Kobani.

Speaking by telephone, he estimated Islamic State controlled less than 20 percent of the town. Last month, officials said Islamic State controlled around 40 percent as it pushed further into the town.