Congress 'playing with fire' on debt ceiling: Lew

US Treasury Secretary Jack Lew warned today that Congress was "playing with fire" as Republicans raised the threat of a US default if President Barack Obama refuses to negotiate on spending.

Speaker John Boehner said the Republican-controlled House would not raise the US debt ceiling without concessions from the White House, staking his position as the government shutdown dragged into day six.

"We're not going to pass a clean debt limit increase," Boehner said in an interview on ABC's "This Week."

"I told the president, there's no way we're going to pass one. The votes are not in the House to pass a clean debt limit. And the president is risking default by not having a conversation with us," he said.

Lew said the United States will run out of its ability to borrow money on October 17, and with only $30 billion cash in hand to meet obligations that can run to $60 billion a day, it will quickly face default.

"I'm telling you that on the 17th, we run out of our ability to borrow, and Congress is playing with fire," he said on CNN's "State of the Union".

"If they don't extend the debt limit, we have a very, very short window of time before those scenarios start to be played out."

The $16.7 trillion US statutory debt ceiling has come increasingly into focus with the two sides deadlocked in a legislative fight originally centered on Republican efforts to defund the Affordable Care Act, Obama's signature health care law.

The US government was forced to shut down on Tuesday for the first time in 17 years after Congress failed to pass a stopgap spending measure to fund government operations.

The House refused to pass a spending bill that did not include the measure to defund Obamacare, and the Democratic-controlled Senate would vote only on a bill stripped of the measure.

In a sign the impasse was expected to continue, the Pentagon yesterday announced it will recall most of its furloughed civilian employees.

The House, meanwhile, unanimously passed a bill to retroactively pay the hundreds of thousands of furloughed government workers, in a bid to ease some of the pressure from an unhappy public.

Obama has insisted he will not negotiate with Republicans until they pass a temporary spending bill reopening the government and agree to raise the debt ceiling.

"For as reckless as a government shutdown is, an economic shutdown that comes with default would be dramatically worse," Obama said in a radio message yesterday.