Hundreds of U.S. paratroopers have arrived in Ukraine to train its forces fighting pro-Russian rebels in the east, the U.S. army confirmed Friday, a move Moscow warned could “destabilize” the country.

“Soldiers of the 173rd Airborne Brigade have been arriving over the last week,” Donald Wrenn, a U.S. army spokesman, told Agence France-Presse. “We will have about 300 soldiers from the brigade on the ground providing the training that will last over the next six months.”

The move raised hackles in Russia, which has accused the United States and the European Union of supporting protests that brought down Ukraine's Kremlin-backed president Viktor Yanukovich last year.

“The participation of instructors and experts from third countries on Ukrainian territory ... of course, does not help to resolve the conflict,” President Vladimir Putin's spokesman Dmitry Peskov said, quoted by Russian news agencies. “On the contrary, it can seriously destabilize the situation,” he said.

Following Yanukovich's ouster and Moscow's annexation of Ukraine's Crimea peninsula, a pro-Russia uprising in east Ukraine sparked a conflict that has killed more than 6,000 people over the past year, according to United Nations figures.

Russia denies it is arming pro-Russian separatists or sending in its troops to fight alongside them, but few outside observers find this claim plausible.

Fighting between the separatists and Ukrainian troops is rumbling on in the east despite a February cease-fire agreement, which has been repeatedly ignored.

The U.S. troops will train the National Guard of Ukraine, a reservist force that was reformed in 2014 to bring volunteers and militias under government control.

“We will be conducting classes on war-fighting functions, as well as training to sustain and increase the professionalism and proficiency of military staffs,” said Major Jose Mendez, operations officer for the brigade.

The U.S. army said Ukraine had asked the U.S. to send the training mission, dubbed Operation Fearless Guardian.

A ground convoy drove from the brigade's base in northern Italy to the Ukrainian military zone in Yavoriv near the Polish border with vehicles and equipment for the training mission. The army stressed the equipment was for use by the U.S. brigade in the training and not to be issued to Ukrainian forces.

The 173rd Airborne Brigade has already trained with Ukrainian forces elsewhere in Europe, as well as within Ukraine in multinational field training exercises in September.

The United Kingdom is also deploying some 75 troops to Ukraine to train government forces there, while Canada announced Tuesday that it will send 200 trainers.

U.S. President Barack Obama has come under pressure from some U.S. lawmakers and military officials to send weapons to help the Ukrainian forces defend themselves, but has so far held back.

Some of his European allies, including Germany, have warned that sending arms would escalate the bloodshed.

Al Jazeera and Agence France-Presse