US President Barack Obama demanded an end to a three-day government shutdown he decried as a reckless "farce," piling pressure on Republicans Thursday to climb down first on a budget impasse.

The US Treasury meanwhile warned of "catastrophic" consequences if there is no deal within weeks to raise the US debt ceiling, and the IMF chief said finding a way out of that next crisis was "mission critical."

Obama traveled to the Washington suburbs to lambaste Republican House Speaker John Boehner, who emerged from a White House meeting late on Wednesday complaining that Obama would not negotiate with him.

"Take a vote, stop this farce and end this shutdown right now," Obama said during a fiery speech in the Maryland suburb of Rockville, which is home to many federal workers laid off in the shutdown.

Branding the crisis a "reckless Republican shutdown," Obama said that Boehner could reopen the government and get hundreds of thousands of people back to work "in just five minutes" by passing a temporary operating budget with no partisan strings attached.

"Speaker John Boehner won't even let the bill get a yes or no vote, because he doesn't want to anger the extremists in his party," Obama said.

The government ran out of money on Monday, after Congress failed to pass a budget, forcing authorities to send all non-essential workers home and to close museums, monuments and national parks that are all popular with tourists.

The Democratic-led Senate had turned back repeated Republican efforts to pass a budget while defunding or delaying Obama's health care law, which is a centerpiece of his political legacy and reviled by Tea Party conservatives.

The talks at the White House between Obama and congressional leaders made no progress, and there is no sign that the dispute will be solved before dragging into a second week.

Attention is increasingly turning to the next fight -- over Congress's responsibility to raise the $16.7 trillion US statutory borrowing limit.

If there is no resolution before October 17, the government could begin running out of money to pay its bills and an unprecedented US debt default could result.

But Republicans are again demanding concessions on Obamacare before voting to raise the debt ceiling, raising fears of unpredictable consequences, which the Treasury said in a report Thursday could plunge the United States into deep recession and rock global markets.

"In the event that a debt limit impasse were to lead to a default, it could have a catastrophic effect on not just financial markets but also on job creation, consumer spending and economic growth," the report said.

"Credit markets could freeze, the value of the dollar could plummet, US interest rates could skyrocket, the negative spillovers could reverberate around the world, and there might be a financial crisis and recession that could echo the events of 2008 or worse."

International Monetary Fund chief Christine Lagarde said finding a way out of the debt limit dead end as soon as possible was "mission critical."

The New York Times reported Thursday that Boehner had privately told House Republicans that he understood the dangers of a default and was ready to pass a debt limit increase with the help of minority Democrats if necessary.

Obama has refused to negotiate with Republicans over raising the debt ceiling, saying Congress is simply authorizing borrowing to pay bills it has already run up and that offering concessions would set a poor precedent for future presidents.

In the minds of key players on Capitol Hill, the government shutdown and the debt ceiling fight have now merged into one massive political crisis.

There was some talk among Republicans that Boehner may try to craft a face-saving way out by reviving a stalled drive for a "grand bargain" on debt and spending with Obama.

But there is skepticism on the Democratic side that there is time to pull together a pact -- following repeated
failed attempts in Obama's first term -- before the debt limit needs to be raised by October 17.

The president was meanwhile wrestling with whether to cancel the rest of an already truncated Asia trip that would see him leave on Saturday for the APEC summit in Bali, Indonesia and the East Asia summit in Brunei.

Going ahead would open him to charges of deserting Washington at a time of national crisis.

But Obama is also keen to demonstrate that political problems at home should not be taken as a sign of weakness abroad, and wants to bolster his signature rebalancing of US military and diplomatic power to the dynamic Asian region.