Police in Malaysia have arrested seven boys suspected of starting a fire at an Islamic boarding school that killed 23 people because students there had allegedly teased them.

Speaking at a televised press conference in Kuala Lumpur, police chief Amar Singh said the boys, aged 11 to 18, had been detained after investigators obtained CCTV footage from a neighbouring building.

The blaze at a three-story "tahfiz" school, where Muslim boys study and memorise the Quran, blocked the lone exit to the dormitory, trapping students behind barred windows. Two adults and 21 teenage students were killed.

Mr Singh said that six of the seven boys had tested positive for drugs. Two of the boys had been detained before, one on charges of vehicle theft, another for rioting, he said.

He gave no details on how the suspects had allegedly been mocked by students at the dormitory.

Officials said the school was operating without a fire safety permit and licence, and that a dividing wall was illegally built on the top floor that blocked the victims from a second exit.

The fire renewed calls for better regulation of religious schools.

Religious schools, mostly privately run, are not supervised by the Education Ministry because they come under the purview of state religious authorities. Local media reported there are more than 500 registered tahfiz schools nationwide but many more are believed to be unregistered.

Data from the Fire Department showed that 1,083 fires struck religious schools in the past two years, of which 211 were burned to the ground.

The worst disaster occurred in 1989 when 27 female students at an Islamic school in Kedah state died when fire gutted the school and eight wooden hostels.