US President Donald Trump launched a fresh attack Saturday on London Mayor Sadiq Khan, calling for him to be replaced as soon as possible.

"LONDON needs a new mayor ASAP. Khan is a disaster - will only get worse!" Trump said on Twitter, days after labeling the mayor a "stone cold loser."

Trump attached his latest comment to a retweet about crime in London -- where three men were killed in the span of 24 hours -- from right-wing columnist Katie Hopkins, who has been widely accused of Islamophobia and in 2015 called migrants "cockroaches."

The president's plane had not even touched down in London early this month for the start of a state visit when he tweeted his "loser" comment.

Khan had criticized the red carpet treatment being given Trump for the visit.

Trump said the mayor should "focus on crime in London, not me." He also made a comment about Khan's height.

Khan, London's first Muslim mayor, had led opposition to Trump's visit, writing a newspaper article in which he compared the US leader to European dictators from the 1930s and 1940s.

At that time, the mayor's spokesman called Trump's tweets "childish" and "beneath the president of the United States."

On a trip to London in July last year, Trump accused Khan of doing "a very bad job on terrorism," linking immigration to a deadly wave of crime in London.

The feud began when Khan, the son of a bus driver who emigrated from Pakistan in the 1960s, criticized Trump's travel ban on people from certain Muslim countries.