BUCHAREST, June 22 (Xinhua) -- Troops, equipment and vehicles belonging to the American "IRONHORSE" Combat Unit started to arrive in Romania and Bulgaria, for a rotation of nine months, in support of the Operation Atlantic Resolve, the Defence Ministry of Romania announced in a press release on Friday.

More than 500 wheeled and tracked vehicles and other equipment are expected to arrive to the "Mihail Kogalniceanu" Air Base in southeastern Romania and the Novo Selo Base in eastern Bulgaria.

"In the coming weeks, residents in these areas may see an increase number of convoys carrying heavy-duty vehicles, such as Abrams tanks and Bradley combat vehicles, on their highways and motorways," said a release of the U.S. Embassy in Romania on Friday.

The rotation of the "IRONHORSE" brigade will begin in Romania, where it will gather all its equipment and military personnel, and then some of the forces will move to Bulgaria, said the American release.

During the rotational deployment in Romania, the "IRONHORSE" will continue to make efforts to strengthen inter-operability through training with the Romanian troops from the air forces and land forces.

Operation Atlantic Resolve is a demonstration of the continued commitment of the United States to the collective security of NATO.

It consists of multinational training exercises and security cooperation activities conducted by maneuver elements throughout Eastern European countries.

The U.S. troops on the Atlantic Resolve mission are deployed on a nine-month rotation.