Two boys aged 14 and 15 have been arrested over the fatal stabbing of teenager Tamim Ian Habimana in south east London.
Police detained the pair on suspicion of 15-year-old schoolboy Tamim’s murder.
Both remain in custody at a police station in south London.
Another 15-year-old male held on Thursday is also being questioned over Tamim’s death in Woolwich on Monday evening.
A spokesman for the victim’s school said students and staff were “devastated” to hear of the “tragic and senseless loss of a child’s life”.
A total of 21 London teenagers have been killed in just over six months, leading to concerns that the grim tally for the whole year will exceed the previous high of 29 in 2008.
Officers were called to reports of a stabbing in Woolwich New Road shortly after 5.20pm on Monday and found Tamim suffering from a single stab wound.
He was pronounced dead at the scene at 6.08pm, despite the efforts of emergency services to save him.
Tamim’s death came hours before the unrelated knife death of another teenager in London.
A 29-year-old man continues to be questioned over the murder of Keane Flynn-Harling, 16, in Lambeth, south London, later on Monday night.
The families of both victims are being supported by specially trained officers.
Detective Chief Inspector Richard Leonard, who is leading the investigation, said Tamim’s family is “reeling from the shock of his death”.
He added: “We have made two further arrests in this investigation and I hope this reassures both Tamim’s family and the wider community of our dedication to bringing justice for his murder.
“My team have been working hard to establish the circumstances of what happened and I urge anyone with information that could aid the investigation to come forwards.
“I continue my plea to anyone with footage or images to upload them to police using the below link. They may be very important to our investigation.”
A spokesman for Harris Academy Greenwich said: “Students and staff were devastated to hear that Tamim Ian, a student at our academy for the past two years, was killed on Monday evening in Woolwich. This is a tragic and senseless loss of a child’s life.
“Tamim had been one of our students for the past two years and would have sat his GCSEs next year. Our thoughts and condolences are with Tamim’s family and we will do everything we can to support them at this time.”