Rizwan's family has offered a �10,000 reward to catch his killers

Rizwan Darbar, 17, was stabbed in West Ham Park, Plaistow, east London, on Sunday when he tried to stop a gang stealing a friend's mobile phone.

He was the 20th teenager to have died as a result of gun or knife-related crime in London this year.

The 17-year-old boys have been taken to an east London police station for questioning, police said.