Police from the Metropolitan Police Bureau (MPB) whisked away the Thai Patriots Network leader as he and others were walking along Phahon Yothin road from Victory Monument to Sanam Pao to support activists in the southern region who are demanding reforms in the energy sector and a ban on coal-powered plants.
Acting MPB chief Pol Maj Gen Amnuay Nimmano, who was at the scene to direct officers, said they had defied martial law which bans public gatherings of more than five people.
They were taken from the street to the Royal Thai Army Club before being detained at Phaya Thai police station.
The army blocked advocates of energy reforms from marching from Hat Yai district of Songkhla province to Bangkok last week and urged them to submit their demands through the National Reform Council instead of taking the issue to the streets. They were detained at an army camp in Hat Yai on the same charge of violating martial law.