A bomb attack at an anti-government rally injured a security guard at Chaeng Wattana on Thursday night.
The guard, Yuttanon Songthong, 27, was sent to Mongkutwattana Hospital and received treatment for wounds to his right leg and abdomen.
Police said an M79 grenade was fired at the rally site at 10.45pm and the explosion damaged a tent and injured the guard.
A bomb squad collected many pieces of shrapnel at the scene. They suspected that assailants fired the grenade from a CAT Telecom building near the camp.