An Islamic school in south east London has said a fire on the premises was started by intruders.
About 128 pupils and staff were evacuated from Darul Uloom School, in Foxbury Avenue, Chislehurst, on Saturday.
Firefighters were called to the scene at 23:43 BST. Two men were treated for the effects of breathing in smoke.
A school spokesperson said he was "deeply saddened" and the building had previously been targeted by vandals.
He added the intruders had been caught on the school's security cameras.
"We are part of the British community and are deeply saddened by the events that have taken place last night," Sayed Mahmood, school spokesman said.
"We urge the community to stay firm and united in bringing the people responsible to justice."
Police are treating the fire as suspicious, but have urged the public to remain calm and not to speculate about the cause of the blaze.
London Fire Brigade said there was minor damage to the building and 21 firefighters tackled the blaze.
A spokesperson for London Fire Brigade said: "The fire affected a small part of a school building and there was heavy smoke throughout."
Firefighters managed to get the fire under control by 00:37.
Bob Neill, MP for Bromley and Chislehurst, said: "It's obviously something to be concerned about and we need to find out more about it.
"I've spoken to the police and fire and they are investigating.
"It's too early to jump to conclusions and they need to check out the cause."
In a statement the Metropolitan Police asked for "members of the public to remain calm and not to speculate as to the cause of the fire."
They added that there was also an increased police presence around "potentially vulnerable locations" across London to provide reassurance.
Pupils and staff were able to return to the school building on Sunday morning.
According to its website Darul Uloom London was established in 1988.
The premises comprise of "130 boarding rooms in addition to classrooms, dining hall, assembly hall, prayer hall, gym, playing fields... Each room is shared by two boys."
Starting a fire at a school... time of day doesn't matter, it's a boarding school, children will have been in the school! I'm really glad the fire could be put out before it turned into a blaze.