BANGKOK (Reuters) - Six small bomb blasts wounded at least four people in Bangkok on Friday, as the Thai capital hosted a Southeast Asian security meeting with top diplomats from the United States, China and other world powers.

Prime Minister Prayuth Chan-ocha ordered an investigation into the bombs, a blow to Thailand’s image during the high profile event and barely two weeks after his former military junta transformed into a civilian government.

The first small explosions were heard during rush hour, just before 9 a.m. (0200 GMT), at two sites in central Bangkok. Further blasts hit a government complex hosting several ministries in the north of the city.

Four people were wounded, the Erawan Medical Center said.

Three of those hurt were women cleaning the street when what police called a “ping-pong bomb” went off. Pictures on local websites showed them looking dazed and getting treatment from medics.

The other casualty was near the 77-storey King Power Mahanakhon building, one of the tallest in Bangkok. Police Colonel Kamtorn Uicharoen told Reuters a total of six bombs exploded. One was recovered before it blew up.

“My ears were ringing. The sound was so loud,” said motorcycle taxi driver Chokechai Prasongsan, 48.

There was no immediate claim of responsibility.

“I would like to condemn those causing the situation which destroys peace and damages the country’s image,” Thailand’s prime minister Prayuth said on Twitter.

In a message to the public, Prayuth said: “A group of ill-intended people have recently incited violence while the government is propelling the country forward”.

He did not identify the group, but urged Thais to cooperate with security forces.

None of Friday blasts were very close to the regional security meeting venue. China’s top diplomat Wang Yi and U.S. Secretary of State Mike Pompeo are attending the forum.

Bangkok was last hit by a series of small bomb blasts in 2017. One man, a junta opponent, was jailed for planting a bomb that wounded 21 people at a hospital.

Slideshow ( 9 images )

The city’s worst bombing was in 2015 when 20 people were killed in an attack for which two Chinese ethnic Uighur men were arrested.

A low level insurgency in the largely Malay Muslim provinces of Thailand’s far south has left nearly 7,000 people dead since 2004, but violence largely been confined to that region.

Slideshow ( 9 images )

BOMBS RATTLE CITY

Bangkok is currently hosting a regional security meeting of foreign ministers from the Association of Southeast Asian Nations (ASEAN) and their counterparts from world powers including the United States, China and Russia.

Thai foreign ministry official Arthayudh Srisamoot said the blasts had no impact at the summit. Two fake bombs were discovered nearby on Thursday and police said two people had been arrested in connection with planting them.

The bombs rattled the Thai capital, ranked the world’s most visited city by Mastercard last year. The busy Sala Daeng metro station was shut temporarily over a false alarm.

“It has created a climate of terror and in turn it will pile more pressure on the new government and end their honeymoon period,” said Panitan Wattanayagorn, a political analyst at Chulalongkorn University.

Prayuth, who first took power in a 2014 coup, has headed a civilian cabinet since mid-July following an election in March that his opponents said was managed to ensure the generals kept power. The most senior cabinet members all served in the junta.

Prayuth nonetheless won strong support from the United States on Friday, with Pompeo telling an event in Bangkok: “We commend our Thai friends for returning to the democratic fold”.