Russia is warning the U.S. to quit getting involved in its war against Ukraine or face a direct confrontation between the two world powers.

Anatoly Antonov, Moscow's ambassador to the U.S., told Russian news outlet Tass that the "risk of a clash between the two great powers is high," a day after President Joe Biden announced a new $1.8 billion military aid package for Ukraine, including for the first time Patriot surface-to-air missiles.

Russia's Foreign Ministry has said the delivery of the advanced surface-to-air missile system would be considered a provocative step and that the system and any crews accompanying it would be a legitimate target for Moscow's military.

"It's a defensive system," Biden said of sending the missile system. "It's not escalatory — it's defensive."

Ukrainian President Volodymyr Zelenskyy visited Washington, D.C., on Thursday to reinvigorate support for his country in the U.S. and around the world at a time when there is concern that allies are growing weary of the costly war and its disruption to global food and energy supplies.

Congress has directed nearly $50 billion in assistance to Ukraine and on Thursday approved $45 billion in additional emergency assistance to Kyiv after Zelenskyy addressed a joint session of Congress.

Alexander Darchiyev, director of the Foreign Ministry's North American Department, told Tass that he hoped "Washington will heed the voice of reason" and not allow the situation "to escalate to the point of a direct confrontation between Russia and the United States."

"Otherwise, severed diplomatic ties will become a reality, with all due consequences," Darchiyev added, accusing the U.S. of being responsible for starting the process "of destroying bilateral relations."

Darchiyev also blamed Washington for choosing to "self-isolate" from Moscow and was now "trying to shift the blame, as if someone else brought those relations to the point of no return, not the current administration."

Antonov denounced Zelenskyy's visit to Washington as "theatre," and told Tass that the true goal of the Biden administration is to "intensify the U.S. proxy war against the Russian Federation."

"We emphasize that the risk of a clash between the two great powers is high," he said, adding that Zelenskyy's visit and the conversations in Washington have shown "that neither the administration nor Kyiv is ready for peace."

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