Three people have been arrested on suspicion of murder after a 17-year-old was stabbed in the chest in west London on Thursday.
The teenagers – 15, 17 and 18 – are in custody at a London police station.
Police were called to Lanfrey Place, in the West Kensington area, at about 2.15pm and found a teenager with stab injuries.
He was taken to hospital but died a short time later.
Officers believe they know the identity of the victim but he has not yet been formally identified. His family have been informed.
The teenager who died is the sixth person to be fatally stabbed in the UK in the space of a week.
David Martinez, 26, died from stab wounds in Leyton, east London, on Wednesday afternoon.
That incident followed the murders of two 17-year-olds last Friday and Saturday; Jodie Chesney in east London, and Yousef Makki in Greater Manchester.
Police have now arrested a second man over Jodie’s death.
A 50-year-old woman was also found stabbed to death last weekend in Hendon, northwest London.
A 22-year-old man, who was run over by a vehicle before being stabbed in Oxford on 27 February, also died on Wednesday.
At least 39 people have been stabbed to death in the UK so far this year.
The home secretary has vowed to treat knife crime like a disease following an outcry over the number of victims.
Police numbers have fallen by 20,000 in the past decade in England and Wales but the prime minister has denied a direct link to knife crime – a claim disputed by a number of senior figures in policing.
London Mayor Sadiq Khan has also urged Theresa May to take a tougher stance on knife crime.
He told Sky News on Thursday that she must take ownership of a link between school exclusions and rising levels of violence.
:: Any witnesses or anyone with any information on the West Kensington stabbing is asked to call police on 101 or contact via Twitter @MetCC quoting CAD 4136/07MAR.
Crimestoppers can also be contacted anonymously on 0800 555 111 or online at crimestoppers-uk.org.