LONDON (AFP) - A fire which broke out overnight at an Islamic boarding school in Britain is suspected of being a revenge attack for last month's murder of a soldier on a London street, the country's top police officer said Sunday.

Detectives are "working tirelessly" to establish whether the blaze at the Darul Uloom Islamic School in the south-east London suburb of Chislehurst was started deliberately, according to Metropolitan Police Commissioner Bernard Hogan-Howe.

There have been a string of attacks since soldier Lee Rigby was hacked to death in Woolwich, south-east London, on May 22 in a suspected Islamist attack.

Hogan-Howe urged all communities to shun violence. "We should not allow the murder of Lee Rigby to come between Londoners," he said. "These are difficult times for London's communities. The unified response we have seen to his death across all communities will triumph over those who seek to divide us."

Emergency services were called to the school at around 11.50 pm local time (6.50am Singapore time) on Saturday and the fire was extinguished shortly after the arrival of the fire brigade.

More than 120 pupils and staff at the boys school are believed to have been evacuated after the blaze was discovered.

Two people were treated at the scene for smoke inhalation but their ages have not been released. There was minor damage to building at the £3,000-a-year (S$5,830) school which was established in 1988.

A spokesperson for the school was not immediately available to comment.

Police are also investigating a fire at a Somali centre in north-west London last week.

"Detectives are working tirelessly to establish whether these fires were started deliberately, and if so, to catch those responsible," said Hogan-Howe.

The police chief said the force was using its "full range of policing tactics" to protect potential targets.

"In all boroughs across London, there is an increased police presence around locations that might be at risk.

"We will maintain a 24/7 guard of uniformed officers at sites we consider to be at greatest risk," he added.