A blaze that ripped through a school building in South Gloucestershire was started deliberately, it has been confirmed.
Fire crews were called to The Grange School and Sports College on Tower Road in Warmley, at 00.30 GMT on Tuesday.
At its height, 55 firefighters were dealing with the fire that destroyed about half of the buildings.
Avon Fire and Rescue Service said fire investigators had determined the cause of the fire was "deliberate ignition".
Avon and Somerset Police has appealed for anyone who saw "an individual or individuals acting suspiciously in the area" to contact the force.
"Our investigation is at an early stage but we are treating this incident as suspicious," a spokesman said.
"Enquiries, including reviewing any CCTV footage, are ongoing."
The Grange School closed in 2016 after being placed in special measures.
The site had been earmarked for redevelopment by South Gloucestershire Council.