Islamic State insurgents took control on Thursday of most of the western Iraqi town of al-Baghdadi, threatening an air base where U.S. Marines are training Iraqi troops, officials said.

Al-Baghdadi, about 85 km (50 miles) northwest of Ramadi in Anbar province, had been besieged for months by the radical Sunni Islamist militants who captured vast swathes of Iraq’s north and west last year.

“Ninety percent of al-Baghdadi district has fallen under the control of the insurgents,” district manager Naji Arak told Reuters by phone.

Militants attacked al-Baghdadi from two directions earlier in the day and then advanced on the town, intelligence sources and officials in the Jazeera and Badiya operations commands said.

The officials said another group of insurgents then attacked the heavily-guarded Ain al-Asad air base five km southwest of the town, but were unable to break into it.

About 320 U.S. Marines are training members of the Iraqi…