US President Donald Trump has once again criticised London Mayor Sadiq Khan, calling him a "national disgrace" who is destroying the UK's capital.
His comments came after five violent attacks in London in less than 24 hours left three men dead and three injured.
Labour leader Jeremy Corbyn said it was "absolutely awful" Mr Trump was using the "tragedy of people being murdered to attack the mayor".
Police have increased patrols in the capital following the attacks.
President Trump's tweets follow a long-running feud with Khan.
Retweeting a post by right-wing commentator Katie Hopkins about this weekend's violence in London, the president said Mr Khan was "a disaster" and the capital needed a new mayor.
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
Mr Trump later followed it up with another post saying: "He is a national disgrace who is destroying the city of London!"
In response, Mr Khan's spokesman said the mayor's thoughts were with the victims' families and he "is not going to waste his time responding to this sort of tweet".
The mayor was focused on supporting the city's communities and "over-stretched" emergency services, he added.
Mr Khan later tweeted: "Violent crime has no place in our city, and there's no higher priority for me than Londoners' safety."
Violent crime has no place in our city, and there’s no higher priority for me than Londoners’ safety. Our @MetPoliceUK Violent Crime Task Force are working round the clock to catch offenders & remove dangerous weapons from our streets. https://t.co/sJkKIadP4N— Mayor of London (@MayorofLondon) June 16, 2019
Mr Corbyn tweeted in defence of Mr Khan, saying he was "rightly supporting the police to do their job while Katie Hopkins spreads hateful and divisive rhetoric".
Absolutely awful to see @realDonaldTrump using the tragedy of people being murdered to attack the Mayor. @SadiqKhan is rightly supporting the police to do their job while Katie Hopkins spreads hateful and divisive rhetoric. They seek to divide at a time we need to come together. https://t.co/Se3fgWDXUZ— Jeremy Corbyn (@jeremycorbyn) June 15, 2019
These three deaths take the total number of homicides in London in 2019 to 56. Official data shows that this time last year there had been 82 deaths - and 2018 was ultimately the worst year on record in the city for a decade.
How do these figures compare to other places? Donald Trump's home city of New York is often regarded as a comparable city because it has a similar population and shares other characteristics too.
Figures from the Metropolitan Police show 136 homicides were recorded in Greater London in 2018. That works out as a rate of approximately 1.5 killings for every 100,000 people who live in the capital.
New York Police Department statistics show its per capita murder rate was twice as high.
Month-by-month statistics can mislead because crimes don't occur at regular intervals - but this year's rate for New York is, so far, also double London's.
New York is by no means the US's most dangerous city - there are many others which have far higher murder rates.
Police have made 17 arrests - including several boys and a girl - following the five separate attacks.
The first attack was on Friday afternoon in Wandsworth, south London, where an 18-year-old man was stabbed to death.
Ten minutes later 19-year-old Eniola Aluko was shot dead in Plumstead, south-east London.
Two teenagers have since been charged with the murder of the man in Wandsworth, while five people have been arrested on suspicion of Mr Aluko's murder.
A man in his 30s died after he was stabbed in Tower Hamlets on Saturday afternoon.
In the early hours of Saturday two men were stabbed in Clapham and another was stabbed in Brixton.
Deputy Assistant Commissioner Matthew Twist, from the Metropolitan Police, said: "The circumstances, causes and motives for any homicide or serious violence incident are different and unique, and require different investigative strategies and approaches.
"But we are taking a service-wide response and all officers right across London continue to be relentless in our pursuit of those who bring violence to our communities."
President Trump and Mr Khan have clashed many times in the past.
The president called Mr Khan a "stone cold loser who should focus on crime in London" shortly before landing in Stansted ahead of his three-day state visit to the UK earlier this month.
It followed comments from the mayor of London that the UK should not be "rolling out the red carpet" for Mr Trump during his visit.