"Russia alone could end its war today. Until Russia does, we will stand united with Ukraine for as long as it takes," Secretary of State Antony Blinken said in a statement.

The assistance comes from funds already committed by the US Congress. It also includes ammunition for howitzers, anti-tank weapons and the Harm missiles that target electronic transmissions.

"As Russia's unconscionable war of aggression against Ukraine continues at great human cost, we are again reminded of the boundless courage and steadfast resolve of the Ukrainian people, and the strong support for Ukraine across the international community," Blinken said.

Xi was in Moscow to discuss a proposal by China to stop the war that has been met with cynicism by Washington, which sees the plan as a way to validate Russia's gains on the ground.