Donald Trump has rowed back from his "total and complete shutdown of all Muslims entering the US" and said the policy was "just a suggestion".

The presumptive nominee for the Republican nomination softened his stance in an interview with Fox News Radio after Sadiq Khan, London's new mayor who is a Muslim, expressed concern he would not be able to visit the US.

Trump said he would make an "exception" for Khan as he praised the Labour mayor's success. But Khan rejected Trump's offer and said the Republican's views on Islam were "ignorant" and would make the US and the UK "less safe".

Trump's softening comes just before he is due to meet the Republican house speaker, Paul Ryan, a self-proclaimed "compassionate conservative".

Ryan has previously criticised Trump's policy and his campaign more widely. A number of Republican leaders have now backed Trump, despite extensive efforts to support his rivals for the nomination. But Ryan is yet to endorse the Republican candidate, saying he is "not yet ready" to do so.

The shift in stance on the Muslim ban is not the first time Trump has changed his mind on a policy suggestion. Until recently though he has remained resolute. Last week he reiterated the ban, even if it hurt him at the polls.

"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 on May 4.

"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."

However since then Khan has won the London mayoral election and Ryan has refused to endorse his candidacy. Trump will meet Ryan, senator majority leader Mitch McConnell and other senior figures on Thursday in an attempt to resolve differences and unite the Republican party.