Police believe a fire at a block of flats, in which a five-year-old boy was killed and two other people were injured, was started deliberately.
Police were called by the London Fire Brigade at 5.56am on Saturday to reports of a blaze at a residential property in Russett Way, Greenwich, in southeast London.
Three people – a 34-year-old woman and two boys aged five and 14 – were injured and then taken to south London hospitals. The younger child died a short time later.
The three are all related.
Officers do not believe there were any other people inside the address and are ruling out the involvement of a third party, the Metropolitan Police said.
Scotland Yard has not confirmed the identity of the child who died.
A post-mortem examination will be held in due course.
Lead investigator Detective Chief Inspector Laurence Smith said: “We’ve worked extensively at the scene with the London Fire Brigade following this awful incident and can now confirm that the fire inside the address is thought to have been started deliberately.”
He added: “Wider family have been informed and our specialist officers are supporting them as they come to terms with their loss.
“What I need now is for any members of the public who might have information that could assist our investigation to make contact, so that we can increase our understanding of what has led to this tragic incident and provide the family with answers to the questions they are asking.
“No piece of information is too small – please call us immediately.”
People with information are asked to call the incident room on 0208 345 3985 with the reference Operation Tampere or CAD1321/06MAR, call 101 or tweet @MetCC.
Information can also be given anonymously to Crimestoppers by calling 0800 555 111.