MOSUL, Iraq (Reuters) -At least five rockets were launched from Iraq's town of Zummar towards a U.S. military base in northeastern Syria on Sunday, two Iraqi security sources told Reuters.

       The attack against U.S. forces is the first since early February when Iranian-backed groups in Iraq stopped their attacks against U.S. troops.

       The attack comes on the same day Iraqi Prime Minister Mohammed Shia al-Sudani returned from a visit to the United States and met with President Joe Biden at the White House.

       Two security sources and a senior army officer said a rocket launcher fixed on the back of a small truck had been parked in Zummar border town with Syria.

       The military official said the truck caught fire with an explosion from unfired rockets at the same time as warplanes were in the sky.

       "We can't confirm that the truck was bombed by U.S. warplanes unless we investigate it," said a military official on condition of anonymity because of the sensitivity of the incident.

       The attacks came one day after a huge blast at a military base in Iraq early on Saturday killed a member of an Iraqi security force that includes Iran-backed groups. The force commander said it was an attack while the army said it was investigating and there were no warplanes in the sky at the time.

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       (Reporting by Jamal al-Badrani in Mosul and Ahmed Rasheed in Baghdad; Editing by Andrew Cawthorne and Chizu Nomiyama)