Hundreds of US paratroopers have arrived in Ukraine to train its forces fighting pro-Russian rebels in the east, the US army confirmed Friday, a move Moscow warned could "destabilize" the war-torn ex-Soviet country. "Soldiers of the 173rd Airborne Brigade have been arriving over the last week," Donald Wrenn, a US army spokesman, told AFP. "We will have about 300 soldiers from the brigade on the ground providing the training that will last over the next six months."