London Mayor Sadiq Khan said it was preposterous for Donald Trump to blame a rise in violent crime in the city on immigration after the U.S. president criticised his handling of crime and militant attacks.

"The idea that you can blame this on immigration from Africa is I think preposterous and we should call him out when he does so," Khan told BBC radio on Friday.

Trump told the Sun newspaper that the London mayor had "done a very bad job on terrorism" and referred to "crime that is being brought in" to the city.

"I think he has done a very bad job on terrorism," Trump told the Sun. "I think he has done a bad job on crime, if you look, all of the horrible things going on there, with all of the crime that is being brought in."