US President Donald Trump has called London Mayor Sadiq Khan “a disaster” in response to violence in London, where three men were killed in separate attacks.

Two teenagers were murdered within minutes of each other in different parts of the city on Friday, while a man was stabbed to death on Saturday afternoon.

Retweeting a post by right-wing commentator Katie Hopkins about the killings, the US president said the English capital needed a new leader.

“LONDON needs a new mayor ASAP,” Trump posted.

“Khan is a disaster – will only get worse!”

LONDON needs a new mayor ASAP. Khan is a disaster – will only get worse! https://t.co/n7qKI3BbD2

— Donald J. Trump (@realDonaldTrump) June 15, 2019

The original post by Hopkins called London “Stab-City” and “Khan’s Londonistan” alongside two screenshots of BBC News articles detailing the violence.

A spokesman for Khan said the mayor was focusing on supporting London’s communities and “over-stretched” emergency services.

“He has been in regular touch with senior Met police officers last night and throughout the day,” the spokesman said.

“His thoughts are with the victims’ families. He is not going to waste his time responding to this sort of tweet.”

The US president and London mayor have clashed in the past, including on Trump’s state visit at the start of June.

Trump branded the mayor a “stone cold loser” in a two-part tweet as he touched down in Britain on June 3.

The Labour mayor then accused the president of “playground behaviour” and said he was a “poster boy” for the far-right.

-AAP