Donald Trump has said Muslim migrants are "destroying Europe" as he reasserted his policy to ban them from entering the United States.

During an interview after his recent victory in Indiana, the New York billionaire who is the Republican party's presumptive nominee for President, said he did not care if the pledge caused him damage with voters.

"They're destroying Europe, I'm not going to let that happen to the United States," Trump said on Wednesday during an interview on Morning Joe.

"I don't care if it hurts me," he told hosts Joe Scarborough and Mika Brzezinski. "I'm doing the right thing.

"I've been guided by common sense, by what's right," he continued.

"We have to be careful. We're allowing thousands of people to come into our country," he said. "Thousands and thousands of people being placed all over the country that, frankly, nobody knows who they are."

He added: "We don't know what we're doing."

Trump is now certain to become the Republican nominee for President after his two remaining rivals, Ted Cruz and John Kasich, quit the race.

The idea for Muslims to be banned from entering the US was announced by Trump after the San Bernardino terror attacks.

"Donald J. Trump is calling for a total and complete shutdown of Muslims entering the United States until our country's representatives can figure out what is going on," he said in the aftermath of the attack where two ISIS supporters shot dead 14 people.

He later clarified he only meant Muslims who were not US citizens.

David Cameron has refused to apologise after calling Trump "stupid and wrong". He will visit the UK in August for a fundraising bid. Downing Street has said the Prime Minister would meet Trump but had "no intention" of withdrawing his comments made in the House of Commons in December.

Trump's spokesman said there were "no hard feelings" and that "once nominee, Mr Trump would entertain an invitation from Mr Cameron".