Republicans appeasing 'extremists' on shutdown: Obama

US President Barack Obama has accused Republicans of pandering to the "extreme right wing" of their party and holding Americans hostage in a budget dispute threatening to shutter the government.

Just over six hours before federal services grind to a halt and hundreds of thousands of federal workers are furloughed, Obama yesterday said time was running out for a last-minute compromise.

Republicans in the House of Representatives are seeking to force Obama to delay or defund his signature health insurance reform law in return for funding government operations.

They are using a similar tactic as Obama asks Congress to raise the $16.7 trillion US debt ceiling. If no deal is reached, the United States may begin defaulting on its debts by the middle of October.

"One faction of one party in one house of Congress in one branch of government doesn't get to shut down the entire government just to refight the results of an election," Obama said.

"Congress needs to keep our government open, needs to pay our bills on time, and never, ever threaten the full faith and credit of the United States of America.

In a bid to nudge Congress to an agreement, the president made separate phone calls Monday to congressional leaders, including Republican House Speaker John Boehner, to urge them to pass a funding bill "that doesn't include any extraneous ideological riders," according to the White House.

But the differences on Capitol Hill were stark, with the House late Monday voting for a third time in recent days to attach an anti-Obamacare provision to a stopgap budget measure.

The Senate rejected the previous two and Senate Majority Leader Harry Reid said the latest change would be dead in the water as well.

"Time is running out," Obama said.

"My hope and expectation is that in the 11th hour once again, that Congress will choose to do the right thing and that the House of Representatives in particular will choose the right thing.

"Unfortunately, right now, House Republicans continue to tie funding of the government to ideological demands like limiting a woman's access to contraception or delaying the Affordable Care Act, all to save face after making some impossible promises to the extreme right wing of their party."

Obama also warned that the imminent shutdown would have real and dramatic economic consequences for thousands of Americans and said it was not fair that people who had dug out of the worst recession in decades were again facing economic uncertainty.