BANGKOK (AP) -- A bomb exploded at an army-run hospital in Bangkok on Monday, the third anniversary of a military coup, and authorities said more than 20 people were wounded.
Investigators found remnants of batteries and wires at the scene of the blast on the ground floor of Phramongkutklao Hospital, said Srivara Ransibrahmanakul, the deputy national police chief.
"We can confirm at this stage that it is a bomb," he said.
The blast wounded 21 people, one of them severely, said Lt. Gen. Saroj Kiewkajee, a hospital official. Thirteen were discharged soon after the explosion.
Earlier, police said 25 people had been wounded.
It was not immediately clear who was behind the explosion or if it was connected to the anniversary of the 2014 military coup that overthrew a democratically elected government.
"Please don't connect this with any other incidents because they may or may not be connected,"said Sansern Kaewkumnerd, a government spokesman. "We have to wait for officials to investigate details from surveillance cameras in the area."
Phramongkutklao is a military-run hospital that is also open to civilians. The blast radius from the explosion was 2 to 3 meters (up to 9 feet), police said.
Since the 2014 coup, at least six explosions have occurred in Bangkok. Last Monday, a bomb went off in front of the country's National Theater. Last month, a similar explosion took place in front of an old government lottery office.
Most of the bombs in Bangkok caused only minor damage except for a blast on August 17, 2015, that killed about 20 people near a popular Hindu shrine.