However, a separate fire in a Chiang Mai school yesterday was believed to be an accident and not related to any "undercurrent" political movement.

Police detained Thien Rodkhiew, 46, kamnan of Tambon Khao Kirit, at Kamphaeng Phet police headquarters yesterday morning. Provincial Police Region 6 commissioner Lt-General Adisorn Nonsi personally took part in Thien's interrogation in the afternoon.

Thien is known to have been close to a former police general who was an aid of ousted Prime Minister Thaksin Shinawatra.

Thien's 44-year-old brother, Thong Rodkhiew, was arrested on October 7 for involvement in the September 27 arson attacks on five schools in Lan Krabue and Sai Ngam districts.

Meanwhile, a fire broke out in Wat Srikham Chompu School in Chiang Mai's Saraphi district yesterday morning.

Fire-fighters with four fire trucks took half an hour to extinguish the flames, which caused Bt250,000 worth of damage to classrooms and a first-aid room.

After being alerted by a sixth-grader, school director Preeda Yanasak found sparks coming from a classroom's electrical cut-off switch. Teachers quickly led 300 students from five classrooms out of the building and called police.

Police later summoned the school's director, a janitor and the sixth-grader who first spotted the fire. The boy claimed he saw the fire when he entered the empty classroom to get some paper for making lanterns. Officers noticed carbon residue on the boy's hands, which he said came from setting off firecrackers outside of the school buildings.

Police suspect the fire was caused by either a short circuit or an accident initiated by the child.

Provincial Police Region 5 deputy commissioner Maj-General Phanwat Sriwalai said the scene would be investigated for evidence of arson but considered that unlikely, since the incident occurred in broad daylight.