President Joe Biden will meet with Republican House Speaker Kevin McCarthy on Monday for another round of talks on raising the US debt ceiling less than two weeks before a key deadline to avoid default, officials said.

Anxiety was mounting in Washington on Sunday ahead of the June 1 deadline, set by the US Treasury, for Congress to authorize more borrowing, as the two sides appeared nowhere near a compromise.

Speaking at a press conference before leaving to return to Washington from the G7 summit in Hiroshima, Japan, Biden said Republicans' latest demands for spending cuts as a condition for raising the US government borrowing authority were "frankly unacceptable."

"It's time for the other side to move from their extreme positions," he said.

Biden spoke with McCarthy later from Air Force One as he flew home from Japan. The White House announced Biden would meet with McCarthy on Monday for face-to-face discussions.

For his part, McCarthy said his position remained unchanged.

"Washington cannot continue to spend money we do not have at the expense of children and grandchildren," he said on Twitter after talking to Biden.

In his comments in Japan Biden voiced hope that "we can reach an agreement." However, he cautioned that he could not "guarantee that they wouldn't force a default by doing something outrageous."

Biden said that he was looking into an obscure constitutional clause in the 14th Amendment, which states that the validity of public debt "shall not be questioned" – and potentially authorizing the president to circumvent Congress and raise the debt ceiling himself.

"I think we have the authority. The question is could it be done and invoked in time," he said, noting the likelihood of legal challenges to this and the rapidly approaching debt deadline.

The Treasury Department says that the government could run out of money and default on its $31 trillion debt as early as June 1 if Congress, where Republicans control the House of Representatives, does not authorize more borrowing.

US Treasury Janet Yellen said Sunday on NBC that June 1 remains a "hard deadline." (AFP)