US Republican presidential candidate Donald Trump has challenged London Mayor Sadiq Khan, saying “he was not stupid” and his IQ level is quite better.

In an interview with “Good Morning Britain” host Piers Morgan, Trump criticised Khan, calling him “ignorant” and demanded an IQ test. The comments came following Trump and Khan’s exchange in the Muslim ban arguments. Khan became the first Muslim to head a major European capital in April. The victory was announced amidst Trump’s campaign to ban Muslims travelling to the United States.

On Khan’s triumph, the US presidential candidate expressed his “happiness,” saying that Khan would be exempted from the ban on the entry of Muslims in the US. The London mayor reacted to the comments put forth by Trump as “straight out of the Donald Trump playbook.” He did not only refuse Trump’s exemption offer but also invited him to London.

“I want Donald Trump to come to London so I can introduce myself to him as a mainstream Muslim, very, very comfortable with Western liberal values, but also introduce him to hundreds of thousands, dare I say millions of Muslims in this country, who love being British, love being Western,” Khan said as quoted by Think Progress.

Sadiq Khan also identified the risk that the community is being exposed to because of the comments made by Trump. “Donald Trump’s ignorant view of Islam could make both our countries less safe — it risks alienating mainstream Muslims around the world and plays into the hands of the extremists,” he added.

The series of argument continued as Trump responded to the mayor’s comments in the interview and challenged the latter to an IQ test, according to “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 told the host.

“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.”