Four knife murders in 24 hours in London "graphically illustrates" the need for everyone to pull together and end the violence, Sir Ian Blair has said.
The Scotland Yard head said his officers were doing "everything possible" to catch those responsible and help defend others from the same fate.
Sir Ian spoke out after it emerged a fifth man was fighting for his life in hospital after he was stabbed in an attack in Willesden, north west London.
The man, in his late 20s, was found at an address in Brenthurst Road with stab wounds to the back and stomach.
The four murders took place with 17 hours of each other in Edmonton, Leyton, Walthamstow and Tottenham.
Sir Ian said: "There has been a tragic death toll from knife crime in London over a 24 hour period.
"Four men have been killed - one a teenager - and a fifth remains critically ill. Each is an absolute tragedy and my thoughts are with the families and friends of the victims.
"These attacks are not connected nor do they all involve teenagers. Detectives have made arrests in three of the four murders.
"I want to reassure the public that the Met is doing everything possible both in terms of thoroughly investigating each case and in continuing to carry out proactive operations to get knives off the streets.
"The dreadful loss of life in just 24 hours graphically illustrates the need for everyone to pull together to put an end to this unacceptable violence."
