Donald Trump challenges London mayor Sadiq Khan to IQ test

Presumptive Republican nominee Donald Trump has challenged London's mayor Sadiq Khan to an IQ test, saying he was "not stupid" in an interview with Good Morning Britain's Piers Morgan.

Trump's comments came after the newly elected mayor, who is the first Muslim to lead a major European capital, shut down Trump after his suggestion Khan would be exempt from a proposed ban on Muslims travelling to the United States.

Last week, former human rights lawyer Khan, who is the son of Pakistani immigrants, said the issue is bigger than just one person and is about "my friends, my family and everyone who comes from a background similar to mine, anywhere in the world."

Today, Trump hit back in typically bombastic form, challenging the mayor to an IQ test in an interview that also threatened a poor relationship between the two countries who are close allies.

"He doesn't know me, he's never met me, doesn't know what I'm all about. I think they're very rude statements and frankly - tell him I will remember those statements," the Republican said to host Piers Morgan.

"When he won I wished him well, now I don't care about him," he said.

"I mean it doesn't make any difference to me about him, let's see how well he does. Let's see if he's a good mayor."

A spokesman for Khan told the Huffington Post the views of Mr Trump are "ignorant, divisive and dangerous - it's the politics of fear at its worst and will be rejected at the ballot box just as it was in London.

"Sadiq has spent his whole life fighting extremism, but Trump's remarks make that fight much harder for us all - it plays straight into the extremists hands and makes both our countries less safe."

The reality tycoon was also pressed on his relationship with British Prime Minister David Cameron who recently criticised him over the same Muslim ban comments, saying they were "divisive, stupid and wrong".

Cameron has refused to retract the comments despite calls from Trump aides to do so. When asked about the relationship between the two, Trump said: "It looks like we are not going to have a very good relationship. Who knows, I hope to have a good relationship with him but he's not willing to address the problem either."

He also denied being divisive and said he was a "unifier" while saying the pending EU referendum for Britain was something for people to make up their own mind about.