Four teenagers have been arrested in connection with a fire at an Islamic boarding school in London, police said Monday, as they stepped up patrols around Muslim sites in the capital.

The blaze was the second suspicious fire at an Islamic institution in London following the brutal May 22 killing of a soldier near his barracks in Woolwich. Two converts to Islam have been charged with the murder.

A blaze was reported late Saturday at the Darul Uloom Islamic High School in the southeast London suburb of Chislehurst.

Two people aged 18 and two aged 17 were arrested on suspicion of arson late Sunday and taken to a south London police station. They were later bailed to return pending further enquiries.

The fire caused minor damage to a building at the 3,000-a-year pounds ($4,650, 3,500 euros) school and some 128 pupils and staff were evacuated.

Two people were treated at the scene for smoke inhalation but did not need to go to hospital.

Police say there has been a rise in "Islamophobic crime" since soldier Lee Rigby was hacked to death.

Detectives are also investigating a fire at a Somali centre in northwest London last week.

Police commander Simon Letchford said patrols were being increased around potentially vulnerable locations to provide reassurance and deter crime.

"We are working closely with the Muslim community. We've put additional resources outside a number of premises which we think are vulnerable," he told BBC radio.

He said the police were having to deal with more attacks against Muslims in the wake of Rigby's murder, although many of the incidents were verbal abuse.

"We've definitely seen an increase. We normally have about one Islamophobic crime a day across London. And we've seen (now) about eight a day. But we know it is under-reported," he said.

"It tends to be name-calling, normally against individuals who are at a particular location or wearing a particular style of dress, which draws attention to them.

"This is a time now for Londoners to come together after the tragic murder of Lee Rigby."