US lawmakers and Obama administration officials were weighing the impact of a new proposal by a top Republican to avoid default, as high-stakes negotiations to reduce the country’s deficits remained strained.

In a sign of disarray within his own party, and increased pessimism about the potential for a deal, Mitch McConnell, the Republican leader in the Senate, on Tuesday suggested the use of a rare procedural mechanism to allow the president to approve an increase in the US debt ceiling without the support of Republicans.

The unexpected move was greeted by the White House as strong evidence of the commitment of Republican leaders to raising the debt ceiling, underscoring their belief – which is disputed by some rank-and-file conservatives, that a default would have devastating economic implications.