Six bomb blasts went off at a number of locations across Bangkok on Friday, as the Thai capital hosted a key regional security summit.

A seventh device was recovered unexploded, officials said, and the Thai prime minister has ordered an urgent investigation to find the perpetrators.

Four people were injured in the blasts, none seriously, according to a central medical facility. Images from one bomb site showed three street cleaners looking dazed and getting treatment from medics.

The first two explosions took place near metro stations in the city centre, just before 9am during the morning rush-hour, with another blast occurring near the 77-storey King Power Mahanakhon tower.

And shortly afterwards, a blast was heard at a government complex housing several ministries in the northern part of the city. So far there has been no claim of responsibility.

Bangkok explosions: Thai capital hit by six bomb blasts Show all 16 1 /16 Bangkok explosions: Thai capital hit by six bomb blasts Bangkok explosions: Thai capital hit by six bomb blasts Police conduct an investigation at the scene of an explosion in Bangkok AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts Several bombs exploded in Bangkok injuring at least three people, including this motorbike taxi driver Reuters Bangkok explosions: Thai capital hit by six bomb blasts The Thai capital is hosting a regional ASEAN summit attended by top international diplomats including US Secretary of State Mike Pompeo EPA Bangkok explosions: Thai capital hit by six bomb blasts Police Explosive Ordnance Disposal officers on an explosion site in Bangkok Reuters Bangkok explosions: Thai capital hit by six bomb blasts epa07752883 Members of Explosive Ordnance Disposal (EOD) and Thai forensic police officers inspect the area where a small bomb exploded in Bangkok, Thailand, 02 August 2019. At least three bomb explosions were reported in Bangkok during morning peak hour on 02 August. According to media reports, two people have been injured. EPA/RUNGROJ YONGRIT RUNGROJ YONGRIT EPA Bangkok explosions: Thai capital hit by six bomb blasts A policeman walks through the scene of an explosion in Bangkok on August 2, 2019. (Photo by Lillian SUWANRUMPHA / AFP)LILLIAN SUWANRUMPHA/AFP/Getty Images LILLIAN SUWANRUMPHA AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts Onlookers and police gather at a scene of one of the explosions AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts Police Explosive Ordnance Disposal (EOD) officers work following a small explosion at a site in Bangkok, Thailand, August 2, 2019. REUTERS/Soe Zeya Tun SOE ZEYA TUN Reuters Bangkok explosions: Thai capital hit by six bomb blasts A Police Explosive Ordnance Disposal (EOD) officer works following a small explosion at a site in Bangkok, Thailand, August 2, 2019. REUTERS/Soe Zeya Tun SOE ZEYA TUN Reuters Bangkok explosions: Thai capital hit by six bomb blasts A policeman conducts an investigation at the scene of an explosion in Bangkok on August 2, 2019. - Two people were injured as at least two small explosions hit Bangkok, police said, as the political febrile country hosts a regional summit attended by US Secretary of State Mike Pompeo. (Photo by Lillian SUWANRUMPHA / AFP)LILLIAN SUWANRUMPHA/AFP/Getty Images LILLIAN SUWANRUMPHA AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts Police and members of the explosive ordinance disposal unit gather at the scene of an explosion in Bangkok on August 2, 2019. - At least two small bombs exploded in Bangkok on August 2, rattling the Thai capital as it hosted a regional summit attended by US Secretary of State Mike Pompeo and leaving two people wounded. (Photo by Lillian SUWANRUMPHA / AFP)LILLIAN SUWANRUMPHA/AFP/Getty Images LILLIAN SUWANRUMPHA AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts A policeman conducts an investigation at the scene of an explosion in Bangkok on August 2, 2019. - At least two small bombs exploded in Bangkok on August 2, rattling the Thai capital as it hosted a regional summit attended by US Secretary of State Mike Pompeo and leaving two people wounded. (Photo by Lillian SUWANRUMPHA / AFP)LILLIAN SUWANRUMPHA/AFP/Getty Images LILLIAN SUWANRUMPHA AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts epa07753068 A member of the Explosive Ordnance Disposal (EOD) unit inspects a suspicious object hidden on a footpath on Silom road in Bangkok, Thailand, 02 August 2019. Several bombs exploded in Bangkok injuring at least three people while the Thai capital is hosting a regional ASEAN summit attended by top international diplomats. EPA/RUNGROJ YONGRIT RUNGROJ YONGRIT EPA Bangkok explosions: Thai capital hit by six bomb blasts Members of the explosive ordinance disposal unit gather at the scene of an explosion in Bangkok on August 2, 2019. (Photo by Lillian SUWANRUMPHA / AFP)LILLIAN SUWANRUMPHA/AFP/Getty Images LILLIAN SUWANRUMPHA AFP/Getty Bangkok explosions: Thai capital hit by six bomb blasts Forensic police investigators work following a small explosion at a site in Bangkok, Thailand, August 2, 2019. REUTERS/Soe Zeya Tun SOE ZEYA TUN Reuters Bangkok explosions: Thai capital hit by six bomb blasts Security officers stand at the site of a small explosion at a BTS train station in Bangkok, Thailand, August 2, 2019. REUTERS/Soe Zeya Tun SOE ZEYA TUN Reuters

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

“I have instructed officials to take care of public safety and those affected promptly.”

Prawit Wongsuwan, the deputy prime minister, told reporters that police had arrested two suspects, and accused the bombers of trying to “create a situation”.

On Thursday police had found two fake bombs near the venue of the meeting of foreign ministers of the Association of Southeast Asian Nations (Asean). The meeting was not interrupted.

China’s top diplomat Wang Yi and US secretary of state Mike Pompeo are among the regional and global representatives attending the forum.

It was not immediately clear whether the bombings were designed to target the summit, or if they were linked to Thailand’s recent democratic election, in which the country’s military junta formally gave up power – but coup general Prayuth remained in office.

Analysts say the use of small, generally harmless bombs, is a not uncommon part of the Thai political scene, often characterised by power struggles between factions within the country’s highly politicised security forces.

Bombings are usually blamed on those in opposition at the time, though substantial arrests are rarely made.