Iraqi security forces foiled a suicide attack attempt by the Islamic State group and killed 20 to 25 fighters of the extremist group Friday, who were trying to infiltrate al-Asad air base in the Anbar province of western Iraq.

According to U.S. Navy Rear Adm. John Kirby, after some of the ISIS fighters managed to detonate bombs, a second wave of about 15 fighters showed up and tried to reach the perimeter of the base. However, they were immediately engaged by members of the Iraqi army.

“The attempted attack was led, we believe, by at least several … suicide attackers,” Kirby, a Pentagon spokesman, said in a statement, adding that U.S. troops, who are authorized and equipped to defend themselves against any ISIS attack, are stationed at al-Asad air base to train, advise and assist Iraqi forces.

Al-Asad air base is “basically a base of many, many bases inside,” he said. “And at no time were U.S. troops anywhere near the fighting -- at least a couple of miles away. So, they might've heard shots being fired, but that would've been about it.”

Some of the ISIS fighters were wearing Iraqi military uniforms, The Associated Press reported, citing Kirby.

Earlier this week, ISIS fighters had taken control of al-Baghdadi, a town near al-Asad air base, in one of their first successes in months. However, Iraqi forces continue to operate throughout the region, putting pressure on ISIS militants.

It is important to continue the anti-ISIS events in the region as the group has limited ability to reconstitute their supplies after they have been hit and destroyed, Kirby said.

“These guys steal to survive,” the Pentagon said in the statement. “They just move into an area and basically rob banks. And that's how they get a lot of their money. And when they're not capturing new territory, they're not robbing a whole lot of new banks… They do not have the ability to reconstitute strength the way a normal armed force would.”