HUA HIN, Thailand (AP) - Attackers struck a series of tourist resort towns across southern Thailand with homemade explosives and firebombs in some of the worst violence to hit the country since a military coup two years ago. At least four people were killed and dozens wounded, including 11 foreigners.
It was not clear who was behind the attacks Thursday and Friday, which followed a successful referendum held last weekend on a new constitution that critics say will bolster the military's power for years to come.
But the violence appeared aimed at undermining the country's tourism industry, which provides vital income to the government. One small bomb exploded on a beach in Patong on the island of Phuket and four others rattled the seaside resort city of Hua Hin, prompting businesses to shut their doors, streets to empty and anxious tourists to huddle inside their hotels.
Police said firebombs also triggered blazes at markets and shops in six places, including Phuket, Trang, Surat Thani, Phang Nga and a souvenir shop in the tourist town of Ao Nang, Krabi, a seaside province known for its stunning limestone cliffs.
Thailand's economy has sagged since the military seized power in a 2014 coup. But tourism has remained one of the few bright spots, with visitors rising to 30 million in 2015 and more than 14 million having visited by May 2016, according to official figures.
Foreign governments, including the United States, issued warnings urging travelers to use caution and avoid affected areas.
In a televised address late Friday, Prime Minister Prayuth Chan-ocha said the attacks "struck at the hearts of all Thai people."
He said it was unclear who carried them out and that the government would do its best to investigate. Police said earlier they were investigating all leads, but had ruled out links to international militant groups.
Royal Thai Police Col. Krisana Patanacharoen also said it was "too early to conclude" who was behind the attacks. But he said the bombings followed "a similar pattern used in the southern parts of the country" — a reference to a low-level insurgency in the country's Islamic south that has ground on for more than a decade and killed more than 5,000 people.
Southern militants fighting for greater autonomy have carried out sophisticated, coordinated attacks before, but most have hit three provinces in the far south that were not among those targeted this week.
The violence occurred just ahead of the first anniversary of the Aug. 17 bombing of Bangkok's Erawan Shrine, which left 20 dead and injured more than 120 others. Thai authorities said that bombing was revenge by a people-smuggling gang whose activities were disrupted by a crackdown, but analysts suspect it might have been the work of Uighur separatists angry that Thailand forcibly repatriated more than 100 Uighurs to China.
The latest troubles began Thursday afternoon, when a bomb exploded in the southern province of Trang — an area full of beautiful beaches and tourist islands — killing one person and injuring six, according to police.
Then on Thursday night, attackers in Hua Hin hid bombs on a busy street filled with bars and restaurants. One Thai woman was killed and about 20 people were wounded, 11 of them foreigners.
Police said four of the injured tourists were from Germany, two from Italy and one from Austria. The Netherlands said four of its citizens were also wounded. "No political aim justifies violence and attacks on innocent people," German Foreign Minister Frank-Walter Steinmeier said in a statement.
The bombs were hidden inside two potted plants and were detonated by remote control about half an hour apart, said Gen. Sithichai Srisopacharoenrath, the superintendent of police in Hua Hin. He said a Samsung cellphone had been recovered that they believe was used to detonate at least one of the bombs.
On Friday, debris and ball bearings could be seen strewn across the road as police investigated the scene. The blast damaged a pair of phone booths and shattered the window of a nearby Starbucks.
Many shops in the city center closed afterward and normally bustling streets were empty, for good reason: Hua Hin was hit by another two bombs that exploded in quick succession Friday morning near a clock tower, killing one person and wounding four more.
Also Friday morning, separate blasts were reported elsewhere in the south. One exploded on popular Loma Beach in Phuket city's Patong district, injuring one person. Two more detonated half an hour apart in front of two police stations in Surat Thani, killing one and wounding three. And two bombs exploded outside a market in Phang Nga, damaging two vehicles but causing no casualties.
In Hua Hin, 51-year-old Italian Andrea Tazzioli said he "saw light, white light" after the second of Thursday night's explosions, and that he immediately felt pain in his shoulder "like big fire."
Speaking later at a hospital, he said he fell down and saw people "screaming, the glass broken, table broken, confusion."
Tour guide Niels Seeberg had come across the first blast site earlier in the night, and thought it might be a gas explosion. So he and his friends continued on to a venue where a live band was playing.
"We were standing at the very back of the bar and watching the music. Suddenly there was a big blast, a very big blast, and I could feel the pressure on my eardrums," he said.
"The music stopped, everything stopped, everyone froze," he added.
Soon the bar filled with panicked people running from the blast site, some smeared in blood.
"They didn't scream. They were more like numb," he said. "People were shocked, they couldn't say anything."
Thailand has been plagued by political violence, including several bombings, since the populist billionaire Thaksin Shinawatra was ousted as prime minister in a 2006 military coup after demonstrations accused him of corruption, abuse of power and insulting King Bhumibol Adulyadej.
Thaksin's ouster set off sometimes-bloody battles for power between his supporters and opponents, who include the military. The government of his sister Yingluck Shinawatra, who became prime minister in 2011, was toppled in the country's last coup in 2014.
On Sunday, Thai voters approved a referendum on a new constitution that is supposed to lead to an election next year. Critics say it is undemocratic and is fashioned to keep the military in control for at least five more years even if a free election is held.
Friday's blast took place on the birthday of Thailand's Queen Sirikit. The junta has repeatedly said that defending the monarchy is a top priority, and the army and its allies are keen to ensure a smooth succession for Bhumibol, who is the world's longest reigning monarch.
Pitman reported from Bangkok. Associated Press journalists Jerry Harmer in Hua Hin, Tassanee Vejpongsa, Grant Peck, Natnicha Chuwiruch and Vicky Ge Huang in Bangkok, and Alina Hartounian in Phoenix, Arizona, contributed to this report.