A top Russian diplomat said Saturday that Moscow has informed U.S. officials that it views Western arms shipments to Ukraine as "legitimate targets" for military attacks, heightening fears of a direct confrontation between the nuclear-armed powers.

"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," Sergei Ryabkov, Russia's deputy foreign minister, told a state television outlet Saturday morning.