Two dozen jihadists—including at least four suicide bombers—charged at the perimeter of an Iraqi base that is home to U.S. troops on Friday, marking the first such attack by suspected members of the self-proclaimed Islamic State.

The assault on the Ayn al Asad Airbase near the city of Ramadi in Iraq’s Anbar province comes just days after the Islamic State took control of the nearby town of al Baghdadi on the Euphrates River, less than 10 miles away. That ISIS took a town so close to the base had immediately raised fears that the terror group would try to strike at American troops.

During the U.S. war in Iraq, the base was the site of frequent attacks by what was then known as Al Qaeda in Iraq, the group that subsequently renamed itself Islamic State and declared a supposed “caliphate” last year. It is now widely known by the acronyms ISIS or ISIL.

As one Pentagon official explained to The Daily Beast, “We are all too familiar with this kind of attack.”

In the weeks leading up to Friday’s assault, suspected ISIS fighters had launched small-arms attacks, on average, twice a week. None of those had injured a U.S. service member but ISIS may well have been probing the base defenses.

Friday’s attack began at 7:20 a.m. when roughly eight suspected fighters— at least four wearing suicide vests—charged the perimeter of the sprawling complex. The enormous installation, spread out across the desert of restive Anbar Province, covers about as much territory as Boulder, Colorado. There are 400 U.S. troops there, tasked with securing the compound and training 750 Iraqi soldiers.

Some of the suicide bombers blew themselves up, and several behind them tried to storm the gate, the Pentagon said.

According to Rear Adm. John Kirby, a Pentagon spokesman, “they were immediately engaged” by Iraq’s 7th Army Division. There are no initial indications that any Iraqi troops were injured, he told reporters during a briefing Friday.

The U.S. military immediately scrambled Apache helicopters and Predator drones but by the time they were in the air, the incident was over, Kirby said. He added that the closest American soldier was roughly two miles away from the action.

U.S. officials believe all the attackers were killed during the assault, either because they detonated themselves or were killed by Iraqi forces. But they could not say for certain as they had not conducted, as Kirby put, a “nose count.”

The ISIS taking of al Baghdadi, which Kirby said happened over the last several days, dashed hopes that the six-month campaign by coalition forces had thwarted ISIS attempts to take new ground. There was no clearly organized security force in the town and the entire Iraqi security apparatus has been badly fractured, so it appears ISIS faced relatively little resistance.

The incident also comes amid increased fears that ISIS will attempt to kidnap an American in the region. U.S. officials do not believe any other Americans currently are held by the group. Last week, ISIS announced that Kayla Mueller, 26, had been killed in Raqqa during a coalition air strike. The Obama administration later confirmed her death, but not the circumstances.