Boris Johnson has said his successor as London Mayor, Sadiq Khan, must take responsibility for knife crime in the capital.
Mr Johnson, who was mayor until 2016, said it was a “scandal” that the murder rate in London was higher than in New York in February.
In a newspaper article, he accused Mr Khan of blaming “everyone but himself”.
A spokeswoman for the mayor said Mr Johnson’s words were “desperate nonsense”.
Mr Khan has previously blamed government cuts to police budgets for the rise in violent crime.
Writing in the Telegraph, former foreign secretary Mr Johnson said: “It is tragic that so many young lives are again being lost on the pavements of our capital.
“But for my money there is a further outrage – and that is the abject failure of the mayor of London either to grip the problem, or even to take responsibility.”
He added: “He [Mr Khan] blames everyone but himself, when it is his paramount duty to keep Londoners safe.”
Mr Johnson said stop and searches “make a difference” and that it was a “serious mistake” for the Home Office to move away from them in 2015.
Mr Khan has shown support for “targeted” stop and search since the spike in murders earlier in the year.
A spokeswoman for the mayor said Mr Johnson’s article was “nonsense from the man who was in the government that slashed stop and search and funding for our police and preventive services”.
She added: “Sadiq is being tough on crime with extra money for the police and increased levels of targeted stop and search, as well as the causes of crime with money for youth services.
“But he has one hand tied behind his back – what City Hall can do is a drop in the ocean in the face of billions of pounds of government cuts and the mayor makes no apology for calling for more money for our police.”
London is experiencing an upsurge in serious violent crime, particularly among teenagers and young men, although it is not at the levels seen in the mid-2000s.
The number of “knife and sharp instrument offences” fell for three years in a row in the Metropolitan Police area when Mr Johnson was mayor, down from 14,159 in 2010/2011 to 9,680 in 2014/15, according to figures from the Office of National Statistics (ONS).
There was then an increase to 12,061 offences in 2016/17 and 14,695 in the following year.