"The marine was guarding a checkpoint at a medical facility when two men posing as landscape workers approached. One man shot and killed the marine," Centcom said.

"Marines nearby shot and killed the Syrian man while the second attacker fled the scene."

The Centcom statement said the name of the marine from the First Expeditionary Force was being witheld pending notification of next of kin.

It was not the first time that US commanders had reported coming up against nationals of other Arab countries in the more than three-week-old war in Iraq.

US commanders have expressed concern about the presence of volunteer fighters from a string of Arab countries, including Syria.

An investigation into the shooting was under way early Sunday, Centcom said.

SPACE.WIRE