The head of Scotland Yard has sought to reassure the public after four men died in separate knife attacks in London in 24 hours - and a fifth remains fighting for his life.
Sir Ian Blair said the killings were not linked - and promised that the Metropolitan Police were doing "everything possible to get knives off the street".
The four murders took place with 17 hours of each other in Edmonton, Leyton, Walthamstow and Tottenham.
A fifth attack took place in Willesden, leaving a man in his late 20s critically ill with stab wounds to his back and stomach.
Sir Ian said: "These attacks are not connected nor do they all involve teenagers. Detectives have made arrests in three of the four murders.
Gordon Brown has described the recent stabbings as "shocking and tragic".
The Prime Minister said in a statement that Home Secretary Jacqui Smith would set out the Government's latest plans to tackle knife crime on Monday.
"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."
Last week Deputy Commissioner Sir Paul Stephenson revealed a 75-strong task force aimed at tackling knife crime.
Thousands of people have been stopped and searched in recent weeks as part of a police drive to deter young people from carrying knives.
Meanwhile, London Mayor Boris Johnson said he would be talking to the Government about bringing forward new measures to tackle the crime.
"We need to do all we can to address the long-term complex root causes of violence as well as ensuring the police are providing an effective deterrent to those who carry knives and guns," he said.
Stabbing updates
- :: Edmonton: Two men have been arrested after a 19-year-old was knifed in a confrontation at a bedsit in Gloucester Road.
- :: Leyton: Detectives are investigating reports that 20-year-old Adnan Patel was stabbed in a road rage incident and tried to flee the scene in his car before crashing. Four people were arrested shortly after the attack.
- :: Walthamstow: a man aged in his 20s was fatally stabbed in the chest and head in an attack in St David's Court.
- :: Tottenham: A man thought to be in his 40s was found stabbed to death at the rear of a disused pub in Tottenham High Road. Two men and a woman were arrested nearby.