The small fires broke out at three spots in the Pratunam area early in the morning, before a series of small bombs targeted the Government complex in Chaeng Wattana, a BTS station and a soi off Rama IX road later in the morning.
The fires were each put out in about a half-hour.
The source said police checking the fire scenes found elements for making homemade bombs at the three sites, leading to the conclusion that they were acts of arson linked to the bomb attacks.