Hours before his first trip to Asia as president, Biden will sit down with Swedish Prime Minister Magdalena Andersson and Finnish President Sauli Niinisto at the White House on Thursday to discuss their NATO applications.

"This is a historic event, a watershed moment in European security. Two nations with a long tradition of neutrality will be joining the world's most powerful defensive alliance," said White House national security adviser Jake Sullivan.

Biden has made uniting Europe against Russia's invasion of Ukraine a top priority. Turkey has raised questions about including Finland and Sweden in the alliance, asking Sweden to halt support for Kurdish militants it considers a terrorist group and both to lift their bans on some sales of arms to Turkey.

Sullivan told reporters on Wednesday that US officials are confident Turkey's concerns can be addressed. All 30 NATO members need to approve any new entrant.

Biden's meeting comes as he seeks approval from the US Congress for $US0 billion in aid for Ukraine to provide weapons and humanitarian assistance through September.

US officials said on Wednesday the United States has collected intelligence showing some Russian officials are aware there are abuses being conducted against Ukrainians in Mariupol.

"Some Russian officials recognise that despite claiming to be 'liberators' of the Russian-speaking city of Mariupol, Russian forces are carrying out grievous abuses in the city, including beating and electrocuting city officials and robbing homes," the official said, citing declassified intelligence.

Russian officials worry these abuses "may further inspire Mariupol residents to resist Russian occupation," the official said.

The Kremlin did not immediately respond to a request for comment and Reuters was unable to verify the intelligence claim.

Australian Associated Press