Barack Obama refused to blink on Thursday in the escalating stand-off over his healthcare reforms, insisting he would not heed Republican calls to negotiate over their twin threats to shut down the government and force a debt default.

"They are threatening steps that would badly hurt our economy," the president said in his first big speech of the latest budgetary stand-off. "That's not going to happen as long as I'm president. The Affordable Care Act is here to stay."

Minutes earlier, Republican leaders in the House of Representatives upped the ante by announcing a new set of demands in exchange for extending the US debt ceiling when it expires in mid-October.

In addition to postponing the implementation of the Affordable Care Act, also known as Obamacare, they are now demanding a host of broader political concessions, including tax reform and energy deregulation, in exchange for agreeing to allow further federal borrowing.

House speaker John Boehner also refused to give any indication how he might resolve the separate clash over the so-called continuing resolution (CR), which would authorise government spending to carry on after the current authorisation expires on Monday night.

The initial Republican plan to link this crucial budget motion with their demands for defunding Obamacare is fast unravelling in the Senate, where a majority of Democrats are shortly expected to pass a so-called "clean" bill, shorn of any threat to healthcare reform.

But a cryptic Boehner press conference left open the possibility that Republicans would drop this demand at the last minute and pursue their demands by threatening the debt ceiling instead.

Asked by a reporter, "will you now accept a clean CR from the Senate to avoid a government shutdown," Boehner replied: "I do not see that happening."

Many commentators took this to mean that Boehner could continue to frustrate passage of the bill, by sending it back to the Senate with new demands attached. "If that's the case, what do you plan on sending back to the Senate to avoid that happening?" Boehner was asked.

Raising his eyebrows theatrically, Boehner suggested it was the government shutdown he did not see happening. "I have made it clear for months and months that we have no interest in seeing a government shutdown," he said. There will be options available to us but there is not going to be any speculation about what we might do or not until the Senate passes the continuing resolution."

Other Republican leaders called on the White House to help them out of what look increasingly looks to be a tactical cul-de-sac.

"The president does not call to say 'let's sit over this', he calls to say he will not negotiate," complained House majority whip Kevin McCarthy. "That's not the same message he gives to world leaders."

Obama gave no ground however during a speech to community groups in Baltimore that was intended to focus attention back on the benefits of his healthcare reforms to the 50 million Americans without medical insurance. "Sometimes you just need to escape Beltway politics," Obama said, dismissing what he called "the antics going on in Congress right now".

"In the wealthiest nation on earth, no one should go broke just because they get sick," he added. "In the US, healthcare is not something for the privileged few."

While much of the speech was familiar, the president spelled out more bluntly than usual what was at stake. "There are parts of the bill that some folks don't like; they help pay for the programme," said Obama. "Wealthiest Americans will have to pay a bit more. Extremely costly healthcare plans will no longer qualify for tax exemptions."

But he insisted that most Americans would come to welcome the reforms, which begin in earnest with the opening of new health insurance exchanges next week. "Even if you didn't vote for me, I'll bet you'll sign up for that healthcare plan," he said. "Once it's working really well, I guarantee you they will not call it Obamacare."

The firm White House response was reinforced by officials, who said the kind of horse-trading over spending and welfare entitlements that characterised previous budget deals would not be countenanced by Obama this time.

"He will not engage in an attempt to extort from him what they could not get from the ballot box," said spokesman Jay Carney.

The press secretary also ridiculed what he said was an "extraordinary list of Republican perennials" now being attached to the debt limit extension. "The only thing I didn't see attached was a birther bill," added Carney in reference to past calls for proof of Obama's citizenship.