The fire which killed 21 children and two adults at a tahfiz school in Kuala Lumpur on Thursday was prompted by "mocking", police said.

Kuala Lumpur police chief Amar Singh said seven teenagers aged 11 to 18 have been arrested over the incident.

"In our investigation, the reason behind the mischief (by fire) was caused by ejek-mengejek (mocking).

"The motive was to cause a fire," Amar said at a press conference in Kuala Lumpur tonight.

However, he declined to reveal more about the nature of the mocking or to speculate on any further motives to preserve the court process.

"With the arrest of these seven suspects, I can confirm that the case is now closed and no other suspect needs to be detained anymore," he said.

Amar said police have secured a seven-day remand against the teen suspects, from Sept 16 to Sept 22.

The seven of them, he said, were remanded under Section 117 of the Penal Code for “abetting the commission of an offence by the public, or by more than ten persons.”

The police had been investigating this case under Section 302 and 435 of the Penal Code for murder and “mischief by fire” respectively, he added.

He said the press conference was called following the viral spread on social media of an alleged investigation report on the case.

The police will also be conducting a separate investigation into the perpetrator of the viral message under Section 203A of the Penal Code for “disclosure of information”, as the perpetrator's action could have an effect on court proceedings.

Elaborating on the arrest of the seven suspects, he said they were identified from CCTV footage given to them by the Muslim Consumers Association of Malaysia (PPIM), whose building was next door to the tahfiz school.

The teenagers were then arrested between 6pm on Sept 15 to 2.30am on Sept 16.

Six out of the seven suspects' urine test results came back positive for ganja use, he added, so there is a high possibility that they were under its influence when the incident occurred. 

Though no drugs were found on the suspects, the police will be looking further into their drug use, he assured.

As such, their clothing, motorcycles and helmets have been confiscated to assist with the investigations, he said.

He also revealed that two of the suspects had past criminal records, one under Section 148 of the Penal Code for "possessing weapons or missiles at riot" and the other under Section 379A of the Penal Code for "theft of a motor vehicle".

Amar also confirmed that a type of accelerant was used in the fire and that two gas cylinders from the kitchen of the tahfiz school on the ground floor were brought upstairs.

Despite the arrest of the suspects, he said they would continue to investigate further to examine all other possibilities.

As to whether the operator of the tahfiz school would be investigated for not having a fire safety permit from the Fire and Rescue Department, he said that it would be investigated by the Kuala Lumpur City Hall (DBKL) instead.

When asked whether the teen suspects will be charged as adults, Amar clarified that it is up to the Attorney-General's Chambers (AGC) to decide on matters related to prosecuting the suspects.

On Thursday morning, a fire broke out at the Darul Quran Ittifaqiyah tahfiz school on Jalan Keramat Hujung in Kuala Lumpur.

The funeral services for those who perished in the fire were held last night in several different locations.

Video filmed by Norman Goh.