Several small bombs have exploded across Bangkok, as Thai capital hosted a regional summit attended by US Secretary of State Mike Pompeo and leaving three people wounded.
A police spokesman said a total of six bombs exploded at three locations and one device was discovered before it detonated.
He said three bombs exploded at the Government Complex in Chaeng Wattana and one failed to go off. Two others blew up in the Chong Nonsiarea.
A bomb also exploded in the Suan Luang district slightly injuring three people.
Thai Prime Minister Prayuth Chan-Ocha condemned those behind the bomb blasts.
There has been no immediate claim of responsibility for the blasts.
"On the bombing this morning, I would like to condemn those causing the situation which destroys peace and damages the country's image.
"I have instructed officials to take care of public safety and those affected promptly," Mr Prayuth said.
The small devices are believed to be so-called "ping pong bombs" around the size of a table tennis ball.
They appeared to be symbolic attacks aimed at embarrassing the government during the major summit but not designed to cause mass casualties.
Bomb disposal experts were deployed around the Mahanakorn Tower - owned by the King Power group that counts Leicester City football club among its assets.
The bombings took place just before a keynote speech by Mr Pompeo, who has joined the Southeast Asian Foreign Ministers meeting, in which he praised Thailand for rejoining the "democratic fold".
Thailand's government urged the media to avoid speculation on the motive for the bombings.