President Joe Biden's administration again warned Sunday of "catastrophic" consequences for the US economy if the country defaults, as negotiations with Republicans over a debt deal are expected to resume in the week ahead.

Alarm bells are ringing over the possibility of a first-ever US default, with uncertainty over the actual date the government would stop being able to pay its bills.

Congressional Republicans are demanding budget cuts in exchange for lifting the so-called debt ceiling, while the White House has insisted for months that the nation's credit should not be up for negotiation.

The two sides have remained at an impasse despite weeks of warnings from government officials and bankers that a default could unleash drastic consequences, including a possible recession and likely global financial contagion.

Treasury Secretary Janet Yellen has warned a default could occur by June 1, while the nonpartisan Congressional Budget Office forecast on Friday the date of June 15.

"We shouldn't be here," Deputy Treasury Secretary Wally Adeyemo said Sunday on CNN's "State of the Union."

"If Congress failed to raise the debt limit by the time of default, we would go into a recession and it'd be catastrophic," he warned.

"The United States of America has never defaulted on it's debt -- and we can't."

Biden has stated he wants a "clean" hike of the debt ceiling, but Republicans are insisting any extension of the country's borrowing authority, currently capped at $31.4 trillion, come with substantial curbs on spending.

"It's time to bring spending levels back to pre-Covid, and then we can talk about raising the debt ceiling," Byron Donalds, a Republican representative from Florida, told FOX News on Sunday.

"If Joe Biden brings nothing to the table, if all he does is sit there with his hands in his pockets... then he's the one leading our nation into default."

Former president Donald Trump has encouraged Republican lawmakers to hold out for a default if Biden doesn't agree to "massive cuts."

- 'Constructive' negotiations -

A much-anticipated new round of debt-ceiling talks between Biden and Republican leaders, including House Speaker Kevin McCarthy, were postponed until the coming week.

Adeyemo acknowledged "constructive" negotiations were ongoing at the staff level, while pushing back on assertions that Biden does not want to address ballooning US debt.

"The president's laid out a plan that includes $3 trillion in debt relief over 10 years," Adeyemo said, referring to Biden's budget request unveiled in March, which featured tax increases on the wealthy and businesses.

Congressional leaders should address ways to hammer out a deal on fiscal policy, "but as we have that conversation, there is no reason we shouldn't raise the debt limit and prevent default in this country, a default that could lead to a massive recession that would cost us millions of jobs," he said.

Lael Brainard, director of the White House's National Economic Council, maintained that a deal would be reached.

"Our expectation is that Congress will do what is necessary" to avoid a default, Brainard, a former Federal Reserve vice chair, told CBS Sunday show "Face the Nation."

Biden addressed the issue on Saturday in Delaware, where he talked briefly to reporters.

"They're moving along," he said of the talks. But while there was "real discussion," he added the two sides were "not there yet."

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