Barack Obama has refused to suspend his election campaign after a challenge from rival John McCain.

Republican Mr McCain announced he was putting his own campaign to become the next US president on hold in order to concentrate on helping to resolve the country's financial crisis.

He urged his Democratic rival to do the same and called for the first presidential debate on Friday to be postponed.

Mr Obama said it was a "critical time for everyone" but added this was "exactly the time" when the American people needed to hear from the presidential candidates in a debate.

The Illinois senator said it was his team who had reached out to the Republicans over a joint statement, and he expressed surprise that Mr McCain had pre-empted the statement by making a television appearance alone.

Economic uncertainty brought on by the collapse of the credit market has become the number one issue leading up to the November 4 presidential election as Congress debates a $700 (£338) Wall Street bail-out.

Mr McCain said he did not believe the current rescue plan would be passed and added that America was "running out of time", comparing the crisis to the terror attacks of September 11 2001.

He said he wanted to go to Washington to discuss the stalled plan with lawmakers rather than take Mr Obama on in a debate in Mississippi.

But Mr Obama said: "Presidents are going to have to deal with more than one thing at a time. I believe that we should continue to have the debate."

He added: "Obviously, if it turns out we need to be in Washington, we've both got big planes, we've painted our slogans on the sides of them, they can get us from Washington DC to Mississippi fairly quickly."

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