A bomb blast at a hospital in the Thai capital, Bangkok, wounded 24 people on Monday, on the third anniversary of a 2014 military coup.
There was no claim of responsibility for the blast at the Phramongkutklao Hospital, which is popular with retired military officers.
"It was a bomb. We found the pieces that were used to make the bomb," Kamthorn Aucharoen, commander of the police's explosive ordnance team, told Reuters.
"Right now, authorities are checking out closed circuit cameras."
Government spokesman Sansern Kaewkamnerd said 24 people had been wounded.