A series of bombing and arson attacks in southern Thailand that killed four people and wounded dozens was orchestrated by a single person, and a man has been arrested in relation to one of the attacks, according to Thai police.
Blasts on Thursday and Friday targeted some of the country's best-known tourist resorts, just days after Thailand voted to accept a military-backed constitution that paves the way for an election at the end of 2017.
"These acts were undertaken by a group in many areas simultaneously, following orders from one individual," Pongsapat Pongcharoen, a deputy national police chief, said on Sunday.
He also revealed that the police have arrested one person in relation to one of the attacks.
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"They charged this person with arson," said Al Jazeera's Florence Looi, reporting from Bangkok.
"He was picked up from an oil rig on Saturday and it's in relation to an arson attack on a supermarket in Nakhon Si Thammarat."
Police gave no further details on who they believe was the "mastermind" behind the attacks and no group has claimed them.
"We do know the name of the person who is in custody in relation to the attack, but not the name of the individual who police say masterminded these attacks," our correspondent said.
Police gave no details on who they believe was the "mastermind" behind the attacks [Yongyot Pruksarak/EPA]
"They have been very thin on details."
Analysts say suspicion would inevitably fall on enemies of the ruling junta aggrieved by the referendum results, or fighters from Muslim-majority provinces in the south of the mostly Buddhist country.
Speaking to Al Jazeera from Hua Hin, Thitinan Pongsudhirak, director of the Institute for Security and International Studies at Chulalongkorn University, said: "I think this has to do with domestic politics. It has something to do with anti-regime sentiments - anti-regime people who want to send a message that they don't like the outcome of the referendum."
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Bombs went off on Thursday and Friday in the upmarket resort of Hua Hin and beach destinations in the south including Phuket, Phang Nga and Surat Thani, a city that is the gateway to popular islands in the Gulf of Thailand.
The wave of attacks came as tourists flocked to the beaches at the start of a public holiday. Several attacks used incendiary devices that hit shops and markets in southern Thai provinces.
In Phang Nga, two devices that authorities believe failed to go off were found on Saturday near a market that was torched in an attack early on Friday.
"One worked and the other two didn't," Phakaphong Tavipatana, the governor of Phang Nga, told Reuters news agency, adding that police hoped to find fingerprints on the defused devices.
Prayuth Chan-ocha, the Thai prime minister, has instructed the police to be thorough and cautious in their investigation, according to authorities.
Thai police have come under fire in the past over investigations into high-profile cases, including the brutal murders of two British backpackers on a tourist island in 2014.
Fears that followers of Thaksin Shinawatra and his sister Yingluck Shinawatra, former prime ministers, could be blamed prompted a senior figure in their Puea Thai Party to issue a sharp denial on Saturday.
The anti-government United Front For Democracy Against Dictatorship (UDD), known as the "red shirt" group and sympathetic to the Shinawatras, condemned the attacks in a statement on Sunday.
The group also criticised the government and political parties over suggestions that the attacks were undertaken by people who rejected the constitution in the referendum. The UDD said the junta may use the attacks as justification to stay in power longer.
Thaksin Shinawatra: Let Thailand return to democracy
Thailand has been divided for more than a decade between populist political forces led by Thaksin, who was toppled in a 2006 coup, and the royalist and military establishment, which accuses him of corruption.
His sister Yingluck swept to power in an election in 2011, before being ousted in another coup led by Prayuth in 2014.
At last Sunday's referendum voters in Thaksin's northeast stronghold voted to reject the constitution, which opponents of the junta said would entrench the military's power and deepen divisions.
Voters in three mostly Muslim southern provinces, where separatists have been fighting with the military for than a decade, also voted against the new constitution.
Source: Al Jazeera and agencies