President Joe Biden on Sunday raised the prospect that he might invoke constitutional powers to prevent a damaging US default, as talks with Republican opposition leaders were locked in stalemate.

"I can't guarantee that they wouldn't force a default by doing something outrageous," Biden said at a press conference at the G7 summit in Hiroshima.

"I'm looking at the 14th amendment as to whether we have the... legal authority" to bypass Congress, he added, referring to a clause that states the validity of public debt "shall not be questioned".