A US government official has warned that the US could run out of funding for Ukraine in two months unless Congress approves a new budget.

White House National Security Council spokesperson John Kirby in a news conference Tuesday urged lawmakers not to let the flow of aid be disrupted.

He said the current congressionally-approved funding would allow the US to help Ukraine "for a couple of months or so."

He stressed, "A lapse in support for even a short period of time could make all the difference on the battlefield."

He added that any lapse in support will make Russian President Vladimir Putin believe that "he can wait us out" and that "he can continue the conflict until we and our allies and partners fold."

Kirby's remarks come after Congress narrowly approved a temporary budget on Saturday, a day before the beginning of the new fiscal year. But funding for Ukraine was excluded because of strong opposition from Republican hardliners.

US President Joe Biden proactively made phone talks with leaders of the Group of Seven nations and other countries close to Ukraine on Tuesday. He told them that US support for Ukraine has bipartisan backing in the Congress.