Police say an inferno at a firework factory near Indonesia's capital that killed 48 people was started by sparks from a welder's torch.

Police spokesman Argo Yuwono says the welder, Subarna Ega, is believed to have accidentally caused Thursday's fire in Tangerang, a satellite city of Jakarta. Ega is in police custody with two other suspects.

Yuwono said at a news conference Saturday that the sparks from Ega's welding struck the fireworks and triggered the flames.

The death toll climbed to 48 after a worker who had suffered extensive burns died in a hospital Saturday.

Police have also arrested the owner and the operational director of the factory, which had 103 employees, for allegedly employing underage workers and violating regional minimum wage standards.