Islamic State fighters attacked a fire base a second time, just two days after engaging in a rocket attack that killed one U.S. Marine and several others.

Operation Inherent Resolve spokesman U.S. Army Col. Steve Warren confirmed to reporters during a press briefing Monday morning that ISIS fighters had breached a security perimeter and engaged in a small arms firefight with Marines stationed at a new fire base in northern Iraq. The attack was an apparent follow up to an ISIS rocket strike Saturday which killed Marine Corps Staff Sgt. Louis Cardin and injured as many as eight others.

The fire base was operational for only a few days before ISIS fired two Katyusha rockets into it. The Monday morning follow-up attack was comprised of a squad-sized group (8 to 14) of ISIS fighters, two of whom were killed in the firefight with Marines. Warren noted that no U.S. or Iraqi personnel were injured in the exchange.

The attack appears to mirror a disruption strategy that ISIS has been utilizing ever since ISF and coalition forces began to retake ISIS-held territory. Warren noted that in Iraqi city of Ramadi, which was retaken in December, squad-sized ISIS units continue to infiltrate the city and conduct brief hit-and-run engagements with security forces. Brief, squad-sized attacks betray ISIS’ lack of an element large enough to retake the city, Warren said.

Located near Makhmur in northern Iraq, approximately 9 to 12 miles from the ISIS front line, the new Marine fire base is unique in that it is “geographically separate” from Iraqi bases and is comprised solely of the U.S. forces. Most of the approximately 3,870 U.S. military personnel in Iraq operate in joint base areas or advise Iraqi Security Forces (ISF) directly. Warren described the position as part of a “base cluster” as opposed to a traditional forward operating base (FOB).

According to Warren, the base houses four 155 mm Howitzer artillery pieces, infantry units and early warning assets from the 26th Marine Expeditionary Unit. The detachment is company-sized at less than 200 personnel and is responsible as acting as force protection for the less than 100 U.S. advisers working with ISF units in the area around Makhmur.

Warren said while he does not consider the new fire base an escalation of U.S. presence in Iraq, he does consider it an “accelerant” in the fight against ISIS. He noted that the detachment’s orders are to “shoot back” when ISIS elements threaten coalition forces and that the detachment “will be able to conduct self defense operations immediately,” without Iraq’s permission if necessary.

When asked by reporters if U.S. forces are under higher threat due to the new base, Warren explained that U.S. forces are “in a dangerous place” when it comes to Iraq, and that such attacks are expected in a war situation. He would not say whether or not the artillery force would accompany ISF once they move to retake the Iraqi city of Mosul, but he did note that in response to the attacks, coalition forces would continue to “improve [our] fighting position.”

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