A U.S. Marine was killed and several more were wounded by enemy rocket fire in northern Iraq Saturday, the Pentagon said.

Pentagon press secretary Peter Cook said more information on the Marines' identities would be provided after their next of kin were notified.

A military official said the Islamic State of Iraq and Syria, or ISIS, fired two rockets at the site of a new training base for the Iraqi army in Makmour, CBS News national security correspondent David Martin reports.

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One of the wounded service members was in critical condition, the official said.

Two Iraqi commanders stationed at the base also reported a rocket attack Saturday, but denied anyone had been hurt or killed.

The U.S.-led coalition has reported that the build-up of Iraqi troops at Makmour in preparation for an assault on the ISIS-held city of Mosul has brought a spike in the frequency of such indirect fire attacks.

The last U.S. service member killed in Iraq was in October 2015.