Joe Biden
US President Joe Biden smiles during a press conference. AFP

President Joe Biden on Wednesday urged the US House of Representatives to vote immediately on billions of dollars in Ukraine aid, as the chamber's Republican speaker hesitates in the face of pressure from Donald Trump and his allies.

"There's overwhelming support for Ukraine among the majority of Democrats and Republicans. There should be a vote now," Biden told reporters after meeting Japan's prime minister.

Biden has proposed a package of $60 billion for Ukraine as it seeks to fight back against a more than two-year-old Russian invasion.

The funds passed the Senate, led by Biden's Democratic Party, but have languished for months in the House where Johnson -- leading a razor-thin Republican majority -- has refused to bring a vote to the floor.

Johnson earlier said he was looking at a "number of avenues" on Ukraine but, after the House reconvened from a break, he remained non-committal on Wednesday.

"House members are continuing to actively discuss our options on the path forward," Johnson told reporters.

"There are a lot of different ideas on that. As you know, it's a very complicated matter at a very complicated time," he said.

"The clock is ticking on it, and everyone feels the urgency of that, but what's required is that you reach consensus on it and that's what we're working on."

Russia has regrouped and gone on the offensive amid the deadlock in sending more US weapons, with Ukraine suffering its first territorial setbacks in months after rationing ammunition due to shortages.

European allies have promised to step up but none have the capabilities of the United States.

British Foreign Secretary David Cameron, on a visit to Washington this week, pleaded for the assistance, saying that Western credibility was on the line against Russian President Vladimir Putin and other adversaries.

The British Conservative made his case directly to Trump, who is running for president again and has previously voiced admiration for Putin while doubting Ukraine will win, but Cameron failed to meet Johnson, with UK government sources citing scheduling issues.

Johnson, who rose from obscurity to take the gavel in October, faces a bid to oust him by far-right firebrand Marjorie Taylor Greene who opposes any compromise with Democrats.

Senate Majority Leader Chuck Schumer blasted the Republicans as transforming the party of Ronald Reagan "little by little into a messaging arm of the Kremlin."

He denounced calls by some Trump-aligned lawmakers to push an agreement in which Russia would retain parts of Ukraine, likening them to the British prime minister who notoriously hailed peace with Hitler after Western powers ceded part of Czechoslovakia to Nazi Germany.

"These modern-day Neville Chamberlains ignore the warnings of history -- autocrats have insatiable appetites," Schumer said.

"If you give an autocrat a little land, he'll seek to take a country. And if you give an autocrat a country, he'll seek to take a continent," he said.

Senate Republican leader Mitch McConnell has vocally supported Ukraine but is stepping down and has acknowledged that the party has shifted on foreign policy.

McConnell also criticized Biden for the early refusal to send some advanced weapons to Ukraine, part of the administration's stated effort to avoid a direct US war with nuclear-armed Russia.

"Starving Ukraine of needed capabilities wasn't a smart way for the Biden administration to avoid escalation, and neither is it a political master-stroke by some of the administration's Republican opponents. It is strategic and moral malpractice," he said.