US presidential hopeful Donald Trump is making it more difficult to confront and defeat extremists, British Prime Minister David Cameron has said.

The billionaire is making the "fundamental mistake" of trying to blame all Muslims for the ideology of a minority, Mr Cameron insisted.

Mr Trump, who is vying to win the Republican nomination, sparked widespread anger after he demanded a block on Muslims entering the US and claimed parts of London were "so radicalised" police were "afraid for their own lives".

MPs spent three hours debating whether the tycoon should be allowed into the country after more than 570,000 people signed a petition asking the government to bar him.

Mr Cameron's warning comes after he last year branded Mr Trump's remarks as "divisive, stupid and wrong".

The interventions are likely to put diplomatic relations between Britain and the US under significant strain if the businessman is elected in the November poll.

Mr Cameron told US website Mic.Com: "I think the problem with what Donald Trump has said, and what some others say too, is they are making a fundamental mistake of trying to blame all of Islam and all Muslims for what is the ideology and the actions of a minority, and I think that's wrong.

"In many ways, it actually helps the extremists, because they want to create a clash of civilisations between Islam and Christianity, or Islam and the West.

"Actually, what's happening is not a clash of civilisations. It is a fight within Islam, where the overwhelming majority rightly see Islam as a religion of peace, and want to live in successful multi-racial, multi-ethnic, multi-faith democracies like ours, and make an incredible contribution to our country, as opposed to a small minority that believe this rhetoric of poisonous extremism, and many of this tiny minority then believing in violence.

"So, what Donald Trump says is, in my view, not only wrong, but actually it makes the work we need to do to confront and defeat the extremists more difficult."