"We warned the United States that the orchestrated pumping of weapons from a number of countries is not just a dangerous move, it is a move that turns these convoys into legitimate targets," Russian Deputy Foreign Minister Sergei Ryabkov told state television.

He said Moscow had warned "about the consequences of the thoughtless transfer to Ukraine of weapons like man-portable air defence systems, anti-tank missile systems and so on."

Ryabkov said Washington had not taken Moscow's warnings seriously and added that Russia and the US were not holding any "negotiation processes" on Ukraine.

President Vladimir Putin sent Russian troops into Ukraine on February 24 and said he aims to "de-Nazify" the country.

Moscow has been hit by a barrage of international sanctions since Putin sent in troops.