Despite Mr McCain's solid lead in the battle for delegates to the Republican nominating convention, which analysts call nearly impossible to overcome, Mr Huckabee insisted on Sunday he was going to fight all the way to the wire.

That stance could increase pressure on moderate McCain to turn rightward, but also exacerbate the divisions in the party when it needs unity against the powerful Democrats.

'When I hear people say it's practically impossible, nothing is impossible,' the former Arkansas governor and Baptist preacher told CBS television on Sunday when asked about his chances.

'This country was built on the impossible. And it's impossible that I'm still in the race. That's what most people would have said a few months ago.'

Showing the force of his evangelical Christian base, Mr Huckabee trounced Mr McCain on Saturday in Kansas's caucuses, winning 60 per cent support against the Arizona senator's 20 per cent.

In Louisiana, Mr Huckabee squeaked out a narrow win, 43 per cent to 42 per cent.

And he narrowly lost the Washington state caucus, which voted 26 per cent for Mr McCain, 24 per cent for Mr Huckabee.

He said on Sunday however that he would launch a challenge to the Washington State caucus results, complaining that far too few of votes were counted when the election was called in Mr McCain's favour.

And he rejected calls for to pull out of the race.

'The fact they're blowing against me hardly motivates me to quit,' he told reporters in Washington.

'It motivates me to play harder. If they think they're getting a chorus of voices that will make me say okay, it's time to leave, they don't know me very well.'

Mr Huckabee remains way behind Mr McCain in the crucial delegate count, with just 234 to Mr McCain's 724 - out of 1,191 needed to clinch the nomination - according to poll-tracker RealClearPolitics.com.

But he refused to concede any inevitability on Sunday.

'I'm prepared to stay in until somebody has 1,191 delegates because that's the magic number at which a person is the nominee of the party,' Mr Huckabee insisted on CBS.

'People in many, many states, including large states like Texas, Pennsylvania, Ohio, and all across this country, Nebraska, North Carolina - they've not even voted,' he said. 'So are we to tell them, 'Forget your vote; we don't even care what you think?'

Mr Huckabee's success has come on the back of the party's conservatives, who have made well-known their disgust with Mr McCain, branding him a 'closet liberal'. Christian conservatives have especially latched onto Mr Huckabee's religious values and opposition to abortion.

'I do think (McCain) has got some challenges with not just the evangelicals, but frankly the economic conservatives, because of his opposition to the (President George W.) Bush tax cuts,' Mr Huckabee said on NBC.

Mr McCain's views on immigration 'were way out of the mainstream and quite unorthodox. He has been often the voice in the wilderness', he added.

Mr Huckabee also argues that his experience as a state governor and his stance for a radical reform of the US tax system would make him a better president.

'I've actually run a government,' he told CBS. 'I think senators have the luxury of taking several issues, maybe two or three, and they can specialise in them.'

'But in terms of seeing the whole playing field, they've never managed the whole field.'

Analysts say Mr Huckabee's refusal to pull out of the race - as did Mr Mitt Romney on Thursday - could deepen the party division between conservatives and Republicans ready to back Mr McCain because he stands the best chance of beating the Democratic nominee in November.

But the conservatives are also said to hope their resistance to Mr McCain could push him to adopt more of their positions, like an absolute opposition to abortion and a crackdown on illegal immigrants.

One widely-reported scenario has Mr Huckabee accepting to be Mr McCain's vice-presidential running mate in the election.

But Mr Huckabee insisted he was not planning to run with Mr McCain - as president or vice-president.

'I don't think Senator McCain would select me anyway. I'm not sure I would select him,' he said.

'There are no discussions for such a thing because, at this point, I'm still running for president. There's no other reason for me to think otherwise.' -- AP