A policeman at the scene of one of the explosions. — AFP Photo

BANGKOK — Two men from Thailand's insurgency-hit south have been arrested and linked to several small bombs which rattled Bangkok yesterday as it hosted a regional summit attended by US Secretary of State Mike Pompeo, leaving four people wounded but not disrupting the diplomatic event.

Thailand, which has a grim history of political violence and is fighting a long-running rebellion in the Muslim-majority south, remains deeply divided after a controversial March election returned a junta to power as a civilian government.

Prime Minister Prayut Chan-O-Cha, who led the former junta, told reporters "there were nine successful or attempted explosions... we haven't ruled out any motives."

Two men from the far south were arrested hours after wires and ball bearings were found in an inactive device outside Thai police headquarters late Thursday.

Police chief Jakthip Chaijinda yesterday afternoon confirmed the men arrested were linked to the Muslim-majority area bordering Malaysia which is in the grip of a 15-year insurgency.

But he said it was "too early" to clearly tie them with the rebellion.

A senior officer with the Metropolitan Police Bureau described the bombs seized yesterday as improvised explosive devices.

"(They are) similar to the ones used in the deep south," Kamthorn Oui-charoen said.

Any connection to the insurgency will cause deep alarm in Bangkok, which has failed to win peace in a conflict which has left more than 7,000 dead.

Occasionally the shadowy rebel cells take their violence outside their region to mark key anniversaries or kickback against specific Thai actions.

Outrage is boiling in the south over the treatment of a 34-year-old rebel suspect who was left in a coma hours after being taken into a notorious military interrogation centre in Pattani province.

The blasts in Bangkok yesterday appeared to be symbolic attacks aimed at embarrassing the government during a major summit but not designed to cause mass casualties.

Small devices -- some believed to be so-called "ping pong bombs" around the size of a table tennis ball -- exploded at several locations across the city, none close to the summit venue.

Officials said four people were wounded.

"Reports are they were 'ping pong bombs' hidden in bushes by the road," said Renu Suesattaya, director of Suanluang district where the first bombs were reported.

Two further explosions 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. —AFP