President Biden has told his counterparts in a number of allied countries that he remains confident that Congress will approve military and humanitarian assistance for Ukraine “for as long as it takes” in spite of opposition among some Republicans that blocked funding over the weekend, a national security spokesman said on Tuesday.

In a call on Tuesday morning, Mr. Biden spoke with the prime ministers of Canada, Italy, Japan, and the United Kingdom, and the presidents of Poland and Romania. The chancellor of Germany and the foreign minister of France also joined the call, along with the leaders of the European Commission, the European Council and NATO.

John Kirby, a spokesman for the National Security Council, said early in the afternoon that Mr. Biden had told the leaders that “we cannot under any circumstances allow America’s support for Ukraine to be interrupted. Time is not our friend.” Mr. Kirby said Mr. Biden made it clear that he did not expect any interruption in U.S. aid to Ukraine, despite Congress’s weekend passage of a 45-day stopgap funding bill that did not include any new aid to the country.

“The president certainly talked to the leaders about the vote over the weekend and expressed to them exactly what I expressed to you,” Mr. Kirby said. “He’s confident that we’re going to continue to have bipartisan and bicameral support up on Capitol Hill.”

The call with foreign leaders was an attempt by Mr. Biden to ease concerns that U.S. support for Ukraine was wavering in the aftermath of the passage of the short-term spending bill.

Mr. Biden, his top aides and congressional Democrats and Republicans have said they are confident that further financial commitments will be agreed to in a final spending bill. But the failure to include more aid for Ukraine in the bill the House and Senate passed highlighted the decreasing willingness of some Republicans to fund Kyiv’s war effort.

A readout of the call from the office of the British prime minister, Rishi Sunak, said that Mr. Sunak had “thanked President Biden for convening the call and for his, and the United States’, leadership in supporting Ukraine.” A summary of the call from German officials said the talks “centered on the firm conviction of all participants to support Ukraine.”

The White House provided few details about the discussion among the leaders.

Mr. Kirby shrugged off the ongoing, chaotic power struggle among Republicans in the House on Tuesday. He said that the president and other White House officials had spoken with House Republicans at all levels and remained confident that there was plenty of support for additional Ukraine funding.

Mr. Kirby said that existing funding would last for “a bit,” which he said could be another month or two, depending on what weapons Ukraine needed in its fight against Russia’s invasion. But he said that the impact on the battlefield would be drastic if the ability to provide weapons was interrupted, even for a day.

“There shouldn’t be any lapse,” he said.

Mark Landler, Christopher F. Schuetze, Gaia Pianigiani and Monika Pronczuk contributed reporting.