Police in the Thai resort of Hua Hin have arrested two men after bomb attacks there and across the country left four people dead.
No further details were given of the detentions in the town, where two people were killed in explosions over the space of 24 hours.
Phuket, a top tourist destination, was also targeted in the attacks.
No group has said it carried out the attacks but suspicion is likely to fall on Islamist separatists.
The timing is sensitive, as Friday is a holiday marking the queen's birthday.
At least 10 foreigners were wounded in the attacks: three Germans, three Italians, an Austrian and three Dutch nationals.
The attackers focused on tourist hotspots:
- Four blasts over 24 hours in Hua Hin where two people died
- Two blasts in Surat Thani where one person died
- Two blasts in the tourist beach town of Patong on Phuket island
- One blast in Trang where one person died
- Blasts in the beach province of Phang Nga
Hua Hin is about 200km (125 miles) from the capital Bangkok while the province of Phuket is in the far south.
Both places, as well as Phang Nga, are known for their scenic beaches. Two bombs went off in front of police stations in Surat Thani within the space of half an hour.
Andrea Tazzioli, an Italian tourist injured in Hua Hin, told the Associated Press news agency from his hospitable bed that a man standing next to him had been killed, so he felt lucky to be alive.
"I was having a drink with other people, some of whom I knew, others I didn't [know], and suddenly there was a huge flash of light and an explosion," he said.
"Immediately, I was hit in my back - luckily I had turned away. It was shrapnel.
"There was blood, people shouting, others injured, one person dead, others shouting, others running away, others crying, others fainting, others who didn't know what to do. Someone helped me. Then the police arrived and I was taken to hospital."
Wendy Herbert, an Australian expatriate who lives in Hua Hin, told the BBC the place was deserted on Friday, adding: "I think it's unfortunate because it's Mother's Day and the Queen's birthday in Thailand, so it's a big kind of event day, where everybody would be out and doing things."
Who could be behind the attacks?
Police said they had detained some suspects but ruled out international terrorism.
"Initial investigations reveal that two types of bombs were used, which are fire bombs and improvised explosive devices, or IEDs," said Royal Thai Police Col Krisana Patanacharoen.
The bombings, he was quoted as saying by the Associated Press news agency, followed a "similar pattern used in the southern parts of the country".
The BBC's Jonathan Head in Bangkok says that if southern rebels are behind these attacks, it would mark a significant change of tactics. The 12-year conflict in the south has killed more than 6,000 people, but has never targeted tourists.
Security has been tightened in the tourist areas and at airports in southern Thailand.
Foreign embassies have advised tourists to be vigilant. The UK Foreign Office has advised people in tourist areas to "exercise extreme caution, avoid public places and follow the advice of local authorities".
Thailand's southern insurgency
- The country's Muslim minority largely originates in the three southernmost provinces of Yala, Pattani and Narathiwat
- Insurgents have been fighting since the early 2000s for an independent Islamic state modelled on the old Malay sultanate of Pattani
- Security forces, government workers and local Buddhist communities have been targeted in drive-by shootings, bombings and beheadings
- The violence has been largely confined to the south
- The Thai military and pro-government vigilantes have been accused of a heavy-handed response, including the torture and execution of prisoners
Why have tourist hotspots been targeted?
The attacks have clearly attempted to strike at Thailand's crucial tourism sector.
"The Thais call it [Hua Hin] a white town because there's so many expatriates who live here," Ms Herbert told the BBC.
"There's a large expat community so the local feeling is, from expats and also from Thais, that this is designed to have maximum impact and damage internationally."
But the choice of Hua Hin as a major target is also symbolic, our correspondent says, being known as a royal city and the king's favoured residence outside Bangkok.
Has Thailand seen similar attacks?
Home-made bombs have previously been used by attackers in Thailand at times of political unrest, but since the military took power in a coup in May 2014 such attacks have been extremely rare.
"The bombs are an attempt to create chaos and confusion," PM Prayuth Chan-ocha said to reporters. "We should not make people panic more."
This comes just days before the one-year anniversary of a bomb blast at the Erawan shrine in Bangkok that killed 20 people. The motive has still not been established.
Last week, Thais voted in a referendum which approved a new constitution that will strengthen the military's influence in politics for many years.