Volodymyr Zelensky cancelled his appearance at a classified briefing with US Congress amid a walkout over funding for the Ukraine war.

The Ukrainian president had been due to address senators ahead of a vote on an emergency aid package that includes more than $60 billion in new military support for Kyiv.

Congress has been split for weeks over military aid to Ukraine, with the White House warning that Russia will make battlefield gains unless Congress agrees to new funds for Kyiv. Several Republicans walked out of Capitol Hill during a debate about the funding on Tuesday night.

It came as Lord Cameron, the Foreign Secretary, is due to visit Washington on Wednesday to hold talks with congressional leaders and White House chiefs over Ukraine and Israel.

Lord Cameron is intervening as the West faces growing disunity over support for Ukraine, while Russia is again on the front foot in the war.

Mr Zelensky was due to brief US senators on the situation in his increasingly desperate bids for more funding and military aid.

But he was forced to cancel due to a “last-minute” hiccup, claimed Chuck Schumer, the Democrat Senate majority leader.

However, the night was dominated by tense wrangling on Capitol Hill, and the briefing quickly descended into turmoil.

Senate Republicans are making support for additional Ukraine funding contingent on Joe Biden accepting reforms to the asylum system and tightened border security - measures the Democrats have already rejected.

Mitt Romney, a Republican senator for Utah, insisted that there must be “security of our border”.

Mr Romney, who was one of a number of Republicans who left the meeting early, said: “There’s nothing new in what they’re describing, and Republicans are saying that there’s support for Ukraine, but there has to be security of our border.”

“They want tens of billions of dollars to help our friends and allies overseas, but they’re not willing to do what’s necessary to prevent a potential crisis at the border,” John Cornyn, a Republican senator from Texas, told the New York Times. “The Biden administration just does not seem to care.”

Lindsay Graham, a Republican senator who has repeatedly voiced support for Ukraine, said Republicans would vote for Ukraine when the issue of “real border security” was addressed.

“Count me in on Ukraine; if we do not help Ukraine and Putin gets away with this, you’ll be in a war with Nato - I got all that,” he told the outlet.

“You will get a robust Republican vote for Ukraine, Israel, Taiwan if you have real border security to deal with what I think is one of the biggest national security problems I’ve seen since I’ve been up here.”

Democrats have accused their Republican counterparts of “holding Ukraine hostage” to their domestic priorities.

Chris Murphy, a Democratic senator from Connecticut, said: “I have lots of domestic issues I care about too. I’m not holding Ukraine hostage to the resolution of health care or gun violence.

“They made a choice to put Ukraine funding in jeopardy and they will all have to live with that choice when Vladimir Putin marches into Kyiv and through into Europe.”

Mr Biden said the failure to support Ukraine was “against US interests”, adding, “it’s just wrong”.

It comes as Janet Yellen, the Treasury secretary, said that the US would be “responsible for Ukraine’s defeat” if Congress fails to approve the Biden administration’s latest multi-billion-dollar funding request for the war-torn country.