The national security adviser expressed optimism Wednesday that lawmakers in Washington will break a month-long logjam and approve tens of billions of dollars in military and economic aid to Ukraine. Russian forces have exploited the shortfall to make some gains in the conflict.

"We will get a strong bipartisan vote in Congress," Sullivan said during a press conference. "We will get that money to you as we should, so I don't think we need to speak about Plan B today." He also acknowledged that the process had "taken too long".

Sullivan said the US would consider the conflict a victory for Ukraine if it emerges from the war as a sovereign, democratic and free country.

He sought to reassure Ukrainians that the US will continue to support them as it did since the first days of Russia's invasion, despite the holdup in Congress. House Republicans have thus far refused to take up a Senate-passed bipartisan measure backed by the White House to fund military aid for Ukraine and Israel, as well as humanitarian assistance for people in Gaza.

"There is wide understanding in the United States that Ukraine matters, that the security and future of Ukraine matters to the security and future of United States of America," Sullivan said. "And that we want to help aid a friend and a partner, but we also want to help ourselves in helping you."

Sullivan's trip was meant "to reaffirm the United States' unwavering commitment to Ukraine in its self-defence against Russia's brutal invasion", said National Security Council spokesperson Adrienne Watson.