An explosion, which seriously injured a boy at a Territorial Army centre, in west London, was caused by a torch bomb which had been deliberately planted
The 14-year-old is in intensive care after losing a hand in the explosion.
The army cadet, who has not been named, underwent surgery overnight after the blast in White City. He is in a stable condition.
It is believed the boy picked up the device from outside and took it inside the TA building, on South Africa Road, where it exploded at around 7.10pm yesterday.
The teenager is at the Chelsea and Westminster Hospital, where his parents are at his bedside.
A hospital spokeswoman said he underwent surgery during the night.
The TA centre is next to the BBC Television Centre in White City and is just yards from a school.
Local councillor Reg McLaughlin said he had received a number of calls from worried residents.