WASHINGTON A debt default would deal significant, unambiguous damage to US national security, negatively impacting military readiness, morale and its capabilities, the top US general told a news conference on Thursday.

"I think there's no doubt whatsoever that there would be a very significant negative impact on the readiness, morale and capabilities of the United States military if we defaulted and didn't reach a debt ceiling thing," said Mark Milley, chairman of the Joint Chiefs of Staff.

"I think it would be very, very significant without a doubt in that absolutely clear, unambiguous implications on national security."

President Joe Biden and Republican House of Representatives Speaker Kevin McCarthy were edging closer on Thursday to an agreement on raising the country's $31.4 trillion debt ceiling, according to a person familiar with the talks.

But some hardline House Republicans have pushed back against any compromise deal and insist any agreement must include sharp spending cuts.

The US Treasury has warned it could run short of funds to cover all its expenses as early as June 1, triggering a economically catastrophic default unless Congress reaches a deal.

Economists say that a default would be economically devastating, shaking financial markets worldwide, pushing borrowing costs high and provoking a deep US recession with soaring unemployment.

(Reporting by Idrees Ali, Doina Chiacu and Phil Stewart; Editing by Alistair Bell)