BANGKOK • A small "ping pong" bomb hidden in a plastic bag exploded in Bangkok yesterday, wounding a street cleaner, police said, after a spate of small bombs in the Thai capital raised speculation about opposition to military rule.

The blast happened a day after the authorities said they had arrested a suspect in connection with last month's explosion at a military-run hospital in Bangkok that wounded more than 20 people.

Police commander in Thonglor district Kajornpong Jitpakpoom told Reuters: "It was in a plastic bag hidden in a bush and the city's cleaning staff went to pick it up and open it. That was when it exploded.

"It doesn't appear to be a deliberate attack. It could be related to students who sometimes use small bombs like this and hide them."

The devices are known as "ping pong" bombs, as they are about the size of a table tennis ball.

Police bomb squad officers were at the scene, the team's chief said, adding that it was too early to provide details.

No group has claimed responsibility for several small blasts in Bangkok in recent months, but speculation has grown that opponents of military rule are making a show of defiance.

Earlier yesterday, the military government suggested that opposition to its rule was behind the hospital bomb attack last month, on the third anniversary of the coup.

"He hates soldiers," Deputy Prime Minister Prawit Wongsuwan told reporters, referring to the arrested suspect, whom he blamed for bomb attacks in Bangkok three or four times since 2007.

A 62-year-old former electrical engineer was interrogated earlier yesterday at Bangkok's 11th Army Circle base, which was used by the military as a temporary prison. He has since been charged with premeditated murder, causing injury to others and illegal possession of explosive materials and weapons.

The hospital bombing followed a small blast that wounded two people on May 15 outside Bangkok's National Theatre and an explosion on May 5 in the city's historic quarter.

The arrested suspect was involved in the two incidents as well as the hospital bombing, police chief Chakthip Chaijinda said late yesterday.

REUTERS