Iraqi soldiers and pro-government fighters check an armored vehicle near the town of Muqtadiyah in Diyala province, north of the capital Baghdad, during a military operation against Islamic State forces Jan. 25. (Younis Al-Bayati/AFP/Getty Images)

Islamic State militants seized parts of a town in Iraq’s western province of Anbar on Thursday, sparking fierce fighting within miles of a military base where hundreds of U.S. advisers are stationed.

Anbar’s provincial council called for “immediate and urgent military reinforcements” after the attack on the town of al-Baghdadi, which began in the early morning. Ayn al-Asad air base — where some 320 U.S. personnel have been training Iraqi troops and tribal fighters — lies five miles west of the town.

The clashes so close to U.S. forces will raise concerns as President Obama makes a formal request for congressional authority to use military force against the Islamic State, a move critics argue could open the door to real engagement with the militants on the battlefield.

Thursday’s fighting also demonstrates the continued ability of the Islamic State to remain on the attack despite coalition airstrikes. Still, U.S. officials maintain that the militants remain largely on the defensive.

In a statement, the U.S. military confirmed that there had been “heavy fighting” in al-Baghdadi on Thursday. It said there was no direct attack on the base, though there were “reports of ineffective indirect fire in the vicinity.”

Sheikh Omar Alwani, a tribal leader based in Anbar’s provincial capital of Ramadi, said his fighters in al-Baghdadi had reported that the Islamic State reached within two miles of Ayn al-Asad before being pushed back by Iraqi security forces and tribal fighters backed by coalition airstrikes.

The attack began with a double suicide bombing at the town’s police station at 5 a.m., he said.

Sulaiman al-Kubbaisi, a spokesman for Anbar’s provincial council, said security forces managed to retake some ground in the town by nightfall, with Islamic State fighters still holding the town’s council building.

Coalition airstrikes had assisted in pushing back the militants, he said.

At one point, the militants controlled 90 percent of the town, a local official told Reuters.

The U.S. military said its ground forces were not involved in the fighting but that Anbar remains under “severe threat” by Islamic State fighters. In December, the Pentagon denied local news reports that U.S. forces were involved in direct combat with Islamic State fighters near the base.

While not tasked with combat, U.S. trainers in Iraq are authorized to use force in self-defense. The Authorization for the Use of Military Force, requested by Obama on Wednesday, would leave flexibility for Special Operations forces to give assistance to local forces, the president has said. It would allow the continuation of airstrikes and training programs in Iraq and Syria for the next three years but prohibits “enduring offensive ground combat operations.”