WASHINGTON >> President Joe Biden and British Prime Minister Rishi Sunak affirmed their support for Ukraine on Thursday, pledging to continue drumming up financial and military aid for Kyiv as fighting intensifies on Russia’s front lines.

Sunak, who made his first visit as prime minister to Washington and is intent on establishing a post-Brexit Britain as a competent and reliable global player, said his country would not turn away from Ukraine. That commitment comes even as both he and Biden face economic headwinds and domestic concerns about the length of the war.

“There is no point in trying to wait us out,” Sunak said at a news conference with Biden in the East Room of the White House, addressing Russian President Vladimir Putin, whom he accused of wrongly assuming that the West would tire of providing support. “We will be here as long as it takes.”

Biden said he was confident that he could persuade a divided Congress to support a new round of funding for Ukraine, though he would not put a dollar amount on the package.

“I believe we’ll have the funding necessary to support Ukraine as long as it takes,” Biden said, adding that a “vast majority” of his critics in Congress would agree that funding Ukraine would be better than allowing Russia to go unchecked.

Sunak’s two-day visit was a high-profile engagement for a 43-year-old leader who has held his office only since October and is eager to establish himself on the world stage. It also presented an opportunity for Biden to deepen his relationship with a young leader who is keenly aware that those in his role have historically been among the closest allies to the American president.

Both men hailed the special relationship between the United States and the United Kingdom, with each taking time to praise the other for leadership on Ukraine. But Sunak, who has been in pursuit of a free-trade agreement with the United States — something that Brexit supporters in Britain promised as an alternative to membership in the European Union — will leave Washington with only a modest pact unveiled by both countries on Thursday.

The agreement, called the Atlantic Declaration, will bring the countries closer on research around quantum computing, semiconductor technologies and artificial intelligence, a field in which developments often outpace efforts to regulate them.

“What it does is responds to the particular opportunities and challenges that we face right now and into the future,” Sunak said of the agreement, when asked if it meant that he had failed on his promise to secure a trade deal. Biden, whose Inflation Reduction Act raised some concerns among allies, said that shoring up manufacturing in the United States and bolstering supply chains would “not hurt any of our allies and friends in terms of the trade pieces.”

Sunak did not receive an easy victory in his soft campaign to replace NATO Secretary-General Jens Stoltenberg who is expected to leave his post in September. Sunak has publicly pushed for his defense secretary, Ben Wallace, to take the job. When a reporter asked if it was time for a British official to serve as the secretary-general, Sunak grinned widely, but Biden did not take the bait.

“That remains to be seen,” Biden said. Earlier in the week, he hosted Prime Minister Mette Frederiksen of Denmark, who is also said to be interested in the job.

Biden had warm words for Sunak when it came to the prime minister’s efforts to bring leaders together over issues raised by artificial intelligence. Sunak is a self-described “techie” who will host a summit on AI later this year.

“We are looking to Great Britain to help make that effort to figure out a way through this so we are in full, total cooperation,” Biden said.

The exchange over AI was met with measured skepticism by experts who noted that the efforts of a post-Brexit prime minister may do little to spur leaders to act.

“A London conference on AI regulation is a good thing,” Peter Ricketts, a former national security adviser to Prime Minister David Cameron, wrote on Twitter. “The Brits are good at convening. But this isn’t the same as leading on norm-setting. The heavy lifting is going on in the US-EU dialogue.”

But others pointed out that Sunak has worked to bring his country closer to an array of allies, including by signing off on a plan with the United States and Australia to develop and deploy nuclear-powered attack submarines.

“Making this whole partnership with the United States and Australia, and even Korea and Singapore, more of a thing is the most natural way he can continue to help Britain punch above its weight,” Michael E. O’Hanlon, a senior fellow at the Brookings Institution, said in an interview.

Biden and Sunak have met several times at diplomatic events in recent months, including over coffee when Biden traveled to Northern Ireland in April. Despite their political differences — Biden is a moderate liberal and Sunak a conservative — both men have a shared leadership style that emphasizes even-keeled diplomacy.

On this visit, Sunak was under pressure to assure doubters in the United States and at home that, after Brexit, Britain remains as reliable an ally as ever. He came to Washington with gifts, including a custom Barbour jacket, a staple of British outerwear, for Biden, and both leaders peppered their meetings with historical knowledge about prime minister-presidential relationships past.

“Prime Minister Churchill and Roosevelt met here a little over 70 years ago, and they asserted that the strength of the partnership between Great Britain and the United States was the strength of the free world,” Biden said. “I still think there’s truth to that assertion.”

This article originally appeared in The New York Times.