At least two small bombs exploded in Bangkok on Friday, rattling the Thai capital as it hosted a regional summit attended by US Secretary of State Mike Pompeo and leaving two people wounded.
Prime Minister Prayut Chan-O-Cha was told of "the bombing incidents and has ordered an immediate investigation", Thai government spokeswoman Narumon Pinyosinwat said, adding "security measures have been tightened. The public is urged not to panic."
Two women were wounded in one explosion just outside the city centre, the Erawan Emergency Centre told AFP.
A second explosion shattered glass near a well known downtown skyscraper, emergency police added.
Bomb disposal experts were deployed around the Mahanakorn Tower -- owned by the King Power group that counts Leicester City football club among its assets.
There were unconfirmed reports of several other devices being found across the city.
The bombings took place just before a keynote speech by Pompeo, who has joined the Southeast Asian Foreign Ministers meeting.
The government urged the media to avoid speculation on the motive for the bombings.
The blasts come weeks after former junta leader Prayut was inaugurated as a civilian prime minister, sparking outcry among many pro-democracy supporters in the deeply politically divided kingdom.
The incidents raise the uncomfortable memory of Thailand's last hosting of the Association of Southeast Asian Nations (ASEAN) in 2009.
Then, protesters from the pro-democracy "red shirt" faction smashed their way into the summit venue in the resort city of Pattaya demanding elections.
Pandemonium ensued, with a number of leaders having to be rescued from a hotel roof by Thai army helicopters while others fled by boat.
Thailand has a long history of political violence linked to mass protests, coups and short-lived governments.