Thai police say they have detained two men for questioning in connection with a series of blasts that killed four people and wounded dozens at popular beach resorts and tourist towns across the country.

Two bombs exploded in the upmarket resort of Hua Hin late on Thursday, killing one woman and wounding more than 20 others. They were followed by two more on Friday morning that killed another person.

A further two blasts struck on Friday in the popular tourist town of Phuket, while two more bombs were reported in the southern provinces of Trang and Surat Thani, in each of which one person was killed.

Police detained two men for questioning on Friday over the attacks on Hua Hin, Police Superintendent Sarawut Tankul, of the tourist police, told the Reuters news agency.

The men were detained because CCTV footage showed them in the area "before, during and after the bombings", he said, declining to give more details.

National police chief Chakthip Chaijinda told reporters in Bangkok on Friday that authorities had received intelligence that an attack was imminent, but police had no precise information on location or timing.

"We just didn't know which day something would happen," he said.

The explosive devices were similar to those used by separatists in southern Thailand, but that did not conclusively show they were the perpetrators, Chakthip said.

Police also ruled out any links to international terrorism, as did Thailand's Foreign Ministry, which said in a statement: "The incident is not linked to terrorism but is an act of stirring up public disturbance."

Speaking to Al Jazeera from Bangkok, journalist Pailin Wedel quoted a police spokesperson as saying there is currently no evidence of any link between the different blasts.

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"They are also sticking to the line that they still do not have enough evidence that there are any links to outside terrorism, southern insurgency or anything that may be [tied] to the current political situation," said Wedel.

Chaos and confusion

Prayut Chan-ocha, the prime minister, called for calm and said that he did not know who was behind the attacks.

"The bombs are an attempt to create chaos and confusion," he said in a conversation with reporters. "We should not make people panic more.

"Why the bombs occurred as our country is heading towards stability, a better economy and tourism - and who did it - you have to find out for me."

Last week, Thailand voted to accept a military-backed constitution despite claims by opponents that it will entrench the military's power and deepen divisions.

The two bombs that went off in Hua Hin on Thursday evening were hidden in potted plants and went off within 30 minutes of each other in the bar district of the popular beach town.

While small bombings are common in Thailand during periods of heightened political tension, there have been few such incidents in the past year and it is rare for touristic areas to be targeted.

Hua Hin is home to the summer palace of Thailand's royal family. The blast came on the eve of Queen Sirikit's 84th birthday and just before the first anniversary of a Bangkok shrine bombing that killed 20.

Authorities were searching for leads on the attackers and a motive behind the latest blasts.

According to staff at local hospitals, German, Italian, Dutch and Austrian nationals were among the wounded.

Thailand is expecting a record 32 million visitors in 2016; the tourism industry is a bright spot in an otherwise lacklustre economy.

Anniversary of attack

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.

The blast struck a crowded Hindu shrine in the heart of Bangkok and stunned the country as the deadliest assault in recent history.

Two Uighur men from western China have been accused of the attack and are due to go on trial later this month.

Both deny any involvement in the bombing and mystery continues to swirl around the case, with authorities failing to catch a number of other suspects or offer a thorough explanation for a motive.

Thailand's military government, which seized power in 2014 after a decade of at times violent political unrest, has touted an increase in stability in the kingdom as a major accomplishment of its rule.

Yet the generals have failed to quell a long-running conflict in Thailand's three southernmost provinces - a region far from Bangkok or Hua Hin.

The conflict is largely contained in the mostly Muslim far south, although violence has occasionally spilled into other areas.