A small bomb blast at a military hospital in the Thai capital, Bangkok, wounded 24 people on Monday, three years to the day since the army seized power in the country.

There was no claim of responsibility for the blast at the Phramongkutklao Hospital, which is popular with members of Thailand’s armed forces and their families and retired military officers. The hospital is also open to civilians.

“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, adding it was not clear who was behind the attack.

“Right now, authorities are checking out closed circuit cameras,” Kamthorn said.

Government spokesman Sansern Kaewkamnerd said 24 people had been wounded. Most of the injured were hit by flying glass, the military’s national security unit said.

Suspicion is likely to focus either on political dissidents opposed to military rule or separatists based in the south of the country, which has a long history of small bombs being used by various political and militant groups, especially during significant anniversaries.

Soldiers cordoned off the hospital’s entrance, a Reuters reporter at the scene said.

Deputy national police chief General Srivara Rangsibrahmanakul said the bomb had been hidden in a container by the entrance of a pharmacy.

Monday is the anniversary of a May 22, 2014, military coup that toppled a democratically elected government and ended months of unrest, including sometimes deadly street demonstrations.

Since the 2014 coup, at least six explosions have occurred in Bangkok.

The junta, known as the National Council for Peace and Order, has been clamping down on dissent and ramped up prosecutions under sedition and royal defamation laws.