BAGHDAD -- A U.S. service member in Iraq who was killed Saturday by an explosive device outside Mosul has been identified as 1st Lt. Weston C. Lee, 25, of Bluffton, Georgia, the U.S. Department of Defense (DoD) said Sunday.

In a statement, the DoD said Lee died "from injuries while conducting security as part of advise and assist support to partnered forces."

An earlier Pentagon statement said he had been killed by wounds sustained in an "explosive device blast," stating further information would be released as appropriate.

Saturday's incident marks the second American military fatality since the start of the Mosul operation against the Islamic State of Syria and Iraq (ISIS) group more than six months ago. In October, just days after the operation to retake Mosul was formally launched, Navy chief petty officer Jason C. Finan, 34, of Anaheim, California died of wounds sustained in a roadside bomb attack north of Mosul.

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Finan was part of a team of advisers assisting Iraq's Kurdish fighters known as the Peshmerga.

The Pentagon has acknowledged more than 100 U.S. special operations forces are operating with Iraqi units in and around Mosul, with hundreds more playing a support role in staging bases farther from the front lines.

The service member killed Saturday is the fifth combat death in Iraq since the U.S. launched military operations against ISIS in August 2014. ISIS fighters began growing in power in Iraq in early 2014 in the country's west and in the summer of 2014 swept across much of the country's north.

Since the beginning of the U.S. campaign against ISIS in Iraq, the number of U.S. troops in the country has steadily grown.

There are now more U.S. forces in Iraq than any time since the 2011 U.S. withdrawal, marking an intensifying war as Iraqi forces and the U.S.-led coalition work to push IS out of the last pockets of territory the extremists control in Iraq.