Donald Trump has warned that he may not have a "very good relationship" with David Cameron after the Prime Minister branded his proposal to ban Muslims from the US as "stupid".
The presidential hopeful also sniped at new London Mayor Sadiq Khan, calling him "ignorant" for comments he made after being elected and warning him: "I will remember those statements".
The presumptive Republican nominee, who is likely to go against Democrat Hillary Clinton in a bid for the White House in November, was speaking to ITV's Good Morning Britain.
On being elected as London Mayor, Khan said Trump was "ignorant" in his views on Islam and he risked harming security on both sides of the Atlantic.
Trump responded: "He doesn't know me, hasn't met me, doesn't know what I'm all about. I think they were very rude statements and frankly tell him I will remember those statements. They are very nasty statements."
He added: "When he won I wished him well. Now, I don't care about him, I mean it doesn't make any difference to me, let's see how he does, let's see if he's a good mayor."
Asked if he was offended by Khan's public denouncement he replied: "Yeah, I am."
Trump denied he was "at war" with Khan, who said the tycoon's "ignorant view of Islam could make both of our countries less safe - it risks alienating mainstream Muslims around the world and plays into the hands of extremists".
Trump said: "I just think it's very rude of him. In fact it's the opposite. I wished him well when I heard he won, he's a Muslim... I think it's ignorant for him to say that."