The US Capitol building in Washington, US.

US lawmakers voted on Tuesday to send a $40 billion aid package to Ukraine, as Washington warned that Russia was likely girding for a long conflict with its neighbour.

The defence, humanitarian and economic funding passed the House of Representatives by 368 votes to 57, with the two parties' leaders having already reached an agreement on the details. It will probably be passed by the Senate by the end of the week or next week.

READ MORE

Ukrainians make gains in east, hold on at Mariupol mill

US, Western Europe fret over uncertain Ukraine war endgame

All the dissenting votes came from the Republican ranks.

"With this aid package, America sends a resounding message to the world of our unwavering determination to stand with the courageous people of Ukraine until victory is won," House Speaker Nancy Pelosi told her Democratic colleagues ahead of the vote.

House Speaker Nancy Pelosi speaks during an event. 

Congressional leaders struck a deal on Monday to release $6.8 billion more than the $33 billion previously requested by the White House to help the Eastern European nation ward off Moscow's invasion.

The financial boost includes an extra $3.4 billion for both military and humanitarian assistance on top of the funding requested by the administration.

If the package passes the Senate as expected, US spending to bolster Ukraine's defences against Russia's invasion and address the ensuing humanitarian crisis will soar to around $54 billion.

The White House applauded Tuesday's vote as a "critical step" toward helping Ukraine "defend their democracy" against Russian aggression.

"As the president said yesterday, we cannot afford any delay in this vital effort," White House press secretary Jen Psaki said in a statement.

Congressional leaders strike a deal on Monday requested by the White House.

"We look forward to continuing to work with Senate leadership to get this bill to the president's desk quickly and keep assistance flowing to Ukraine without interruption."

The aid effort comes as a top US official warned that Russian President Vladimir Putin was preparing for a long war that may not end with Russian victory in the east.

"We assess President Putin is preparing for prolonged conflict in Ukraine during which he still intends to achieve goals beyond the Donbas," Director of National Intelligence Avril Haines said at a hearing on Capitol Hill.

She added that Putin was counting on US and EU resolve to weaken as the conflict continues to cause food shortages and inflation, including spiraling energy prices.

Agence France-Presse