Ukrainian President Volodymyr Zelensky will visit Washington on Tuesday for talks with Joe Biden to press the case for more war aid.

The White House said the trip, at Mr Biden’s invitation, is intended to “underscore the United States’ unshakeable commitment to supporting the people of Ukraine”.

Karine Jean-Pierre, the White House press secretary, added: “As Russia ramps up its missile and drone strikes against Ukraine, the leaders will discuss Ukraine’s urgent needs and the vital importance of the United States’ continued support at this critical moment.”

Mr Zelensky’s visit comes at a time when billions of dollars in aid have been stalled on Capitol Hill. Last week, Senate Republicans blocked a bill which would provide aid for Ukraine and Israel.

They said they would not support the bill providing the aid unless the legislation included provisions for tightening security on its southern border.

Aid for Ukraine was part of a $106 billion emergency supplemental package requested by Mr Biden in October.

Last week, Mr Biden warned of the consequences of withholding aid. “This cannot wait,” he said.

“If Putin takes Ukraine, he won’t stop there,” Mr Biden said. Putin will attack a Nato ally, he predicted, and then “we’ll have something that we don’t seek and that we don’t have today: American troops fighting Russian troops”.

Rounding on Republicans, he added: “Frankly, I think it’s stunning that we’ve gotten to this point in the first place, where Republicans in Congress are willing to give Putin the greatest gift he could hope for.”

Last week, the US State Department was able to announce a more modest $175 million tranche of aid including HIMARS rockets, shells and missiles.

Chris Murphy, a Democratic senator, said on Sunday he expected the White House to get more involved in the negotiations.

However, speaking on NBC’s Meet the Press on Sunday, Mr Murphy said the Republicans’ demands were unreasonable.

He accused them of “playing games with the security of the world” by linking the military aid to US border security measures.

Oleksandra Ustinova, a Ukrainian politician, said aid was critical for the country to sustain its military and other functions of government – including paying doctors’ salaries.

“It’s literally going to be a huge problem because if we do not survive as a state, we cannot win a war,” she said.

Mr Zelensky is also under increasing pressure at home, with polls showing his popularity declining.

Last week, the mayor of Kyiv Vitali Klitschko told a Swiss news website that Mr Zelensky had become increasingly autocratic.

“People see who’s effective and who’s not. And there were and still are a lot of expectations. Zelensky is paying for mistakes he has made,” he said.