A string of bomb attacks hit popular tourist towns across Thailand, leaving four dead and many injured, with authorities Friday ruling out terrorism despite suspicions insurgents in the kingdom's deep south are responsible.
In the normally peaceful resort town of Hua Hin, blood-spattered tourists were treated by rescue workers as forensic teams picked through the rubble, with police scrambling to reassure visitors the situation was under control.
"This is not a terrorist attack. It is just local sabotage that is restricted to limited areas and provinces," national police deputy spokesman Piyapan Pingmuang said in Bangkok.
No one has claimed responsibility for the 11 bombings, and the seemingly coordinated attack across five provinces does not match common patterns of violence in the turbulent nation which is currently under military rule.
Analysts said Muslim insurgent groups could be responsible, but that the targeting of tourists far from their stronghold would mark an unprecedented escalation in a simmering conflict largely contained to the southern border region.
Some observers said that anti-junta forces could be plotting to discredit the regime, which has staked its reputation on bringing stability to the kingdom after a decade of unrest.
"The bombs are an attempt to create chaos and confusion," Prime Minister Prayut Chan-O-Cha told reporters as he called for calm.
Britain and Australia reacted by advising their nationals to avoid public places.
Worst-hit was the upscale resort of Hua Hin which was rocked by two sets of twin bombs in the past 24 hours -- one pair on Thursday night and the second on Friday morning.
Two people were killed and more than 20 wounded, including nine foreigners.
A further two blasts struck Friday at Patong Beach on the popular tourist island of Phuket while three more were reported further south -- two in the southern town of Surat Thani, killing one, and one more blast in Trang, which also left one person dead.
"It was very shocking. There was a loud noise and police were running everywhere, it was terrible," said Michael Edwards, an Australian tourist staying in a guest house in Hua Hin close to where one of bombs detonated.
"I was just surprised that it happened here... now I'm thinking if it's worth staying," he told AFP.
Hua Hin, which lies about 200 kilometres (125 miles) south of Bangkok, is popular with both local and foreign tourists and was for years the favourite seaside retreat of King Bhumibol Adulyadej, the world's longest reigning monarch.
The 88-year-old is currently hospitalised in Bangkok for a number of health issues, a source of anxiety for many Thais and a key factor in the kingdom's past decade of political turmoil.
The blasts erupted on the eve of Queen Sirikit's 84th birthday, which is also celebrated as Mother's Day in Thailand.
Thitinan Pongsudhirak, a political expert with Chulalongkorn University, said the attacks were a "blatant challenge to the military", which has ruled over Thailand since ultra-royalist generals seized power in a 2014 coup.
"A military government like this is supposed to be about law and order," he told AFP.
The attacks came less than a week after the junta saw its draft of a new constitution approved in a referendum, giving the generals a fresh claim to popular legitimacy.
However rights groups criticised the junta's bans on debate and campaigning in the lead up to the poll, calling it far from free or fair.
One region that voted down the constitution was the "deep south" -- the three southern border provinces home to a long-running Muslim insurgency against the majority-Buddhist state.
Zachary Abuza, an expert on Southeast Asian militant groups, said that while the southern insurgents had not carried out coordinated attacks for years, it was possible "a small cell" was behind this assault.
"Whoever has perpetrated these wants to do serious damage to the Thai economy. That is where the junta is the most vulnerable."
Thailand's reputation as the "Land of Smiles" has suffered in recent years from political unrest, including small-scale bombings, and a number of high-profile crimes against foreigners.
But tourists continue to flock to its white, sandy beaches. The kingdom is expecting a record 32 million visitors in 2016 -- a bright spot in an otherwise lacklustre economy.
The latest blasts came just days before the first anniversary of the last major attack on tourists in Thailand -- an August 17 bomb that killed 20 people, mostly ethnic Chinese tourists at a crowded Hindu shrine in Bangkok.
Two Uighur men from western China have been accused of the attack and are due to go on trial this month. Both have denied any involvement.