The troops from the 173rd Airborne Brigade arrived on Tuesday and Wednesday in Yavoriv, western Ukraine, to spend six months training three battalions of Ukrainian troops, said the statement yesterday.
The move is likely to anger Russia, which accuses the United States of backing the protests that brought down the pro-Russian president Victor Yanukovych last year, sparking conflict between those loyal to Kiev and Moscow.
The West accuses Russia of arming the separatists who have taken control of some areas in eastern Ukraine, a charge that Moscow denies.
The conflict has so far claimed more than 6,000 lives, according to the United Nations.
The US troops will train the National Guard of Ukraine (NGU), a reservist force reformed in 2014 to bring volunteers and militia 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," Major Jose Mendez, operations officer for the brigade, which is based in Italy, said in the statement.