ISIS militants, who on Thursday seized most of a western Iraqi town, are now just miles away from an air base where hundreds of U.S. Marines are training local forces, Fox News reported.

President Barack Obama has repeatedly ruled out a ground offensive against the terror group, which calls itself the Islamic State and controls large swaths of territory across Iraq and war-torn Syria. But with the militants a mere 13-minute drive away from the Ain al-Asad Air Base, a confrontation seems increasingly likely.

For months, ISIS fighters besieged al-Baghdadi, which lies about 50 miles northwest of Ramadi in Anbar province, Reuters noted. On Thursday, they attacked from two directions and managed to take the town, intelligence sources and officials in the Jazeera and Badiya operations commands said.

"Ninety percent of al-Baghdadi district has fallen under the control of the insurgents," district manager Naji Arak said.

The militants also attempted to attack the heavily guarded air base but were unable to break in. About 320 U.S. Marines are training members of the Iraqi 7th Division at the facility, which had already been struck by mortar fire in the past.

A Pentagon spokeswoman confirmed the fighting in al-Baghdadi but denied there had been a direct assault on the base. "There were reports of ineffective indirect fire in the vicinity of the base," Navy Cmdr. Elissa Smith said.

Anbar has been a stronghold for ISIS as most towns surrounding al-Baghdadi already fell under the group's control when it rapidly advanced across the Syrian border last summer. In the neighboring country, the militants are a key force in the a civil war against moderate rebels and forces loyal to dictator Bashar al-Assad.

Thomas Lynch, a National Defense University fellow, said the United States needs to pay close attention to the events in western Iraq.

"It bears watching," the retired colonel said.

To threaten the Ain al-Asad air base, militants would have to overcome a perimeter that poses a stiff challenge, Lynch explained. While not impossible, ISIS would need a large number of fighters, and that would make its forces vulnerable to airstrikes.

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