The prime ministers of Sweden, Norway and Finland have called on Thailand to fully investigate why no warning was given before last month's tsunami.
Sweden was particularly hard hit by the tsunami
Swedish PM Goeran Persson said European tourists would find it hard to return to Thailand without such a probe.
The Nordic leaders were speaking in the Thai town of Phuket, following a visit to some of the hardest-hit resorts.
More than 2,000 Finns, Norwegians and Swedes are still missing after Thailand was hit by the huge sea surge.
Sweden, with 52 dead and around 900 missing, has the highest casualty total of countries outside Asia.
Mr Persson, together with his Norwegian counterpart Kjell Magne Bondevik and Matti Vanhanen of Finland, were met at Bangkok airport by Thai Prime Minister Thaksin Shinawatra.
All three Nordic leaders expressed heartfelt thanks to the Thai people for helping their nationals during the disaster, but their message to the Thai authorities was rather different, according to the BBC's Tony Cheng in Phuket.
"We want to see an investigation about the warning of the catastrophe," Goran Persson told a news conference.
"The earthquake came a long time before the tsunami," he said. "Why wasn't there a warning? Who was responsible for that?"
The three prime ministers also said the reconstruction of Thailand's resorts and hotels must be done to higher standards.
Having seen for themselves the devastation at Khao Lak beach, they said it was fundamentally important that buildings had the structural integrity to withstand a future tsunami.
All three countries said they were prepared to offer technical assistance to Thailand, and added that the Thai authorities had promised to continue the search for bodies until all nations involved were satisfied.
They also promised to send more forensic experts to help with the identification of bodies and ensure a faster process for the repatriation of victims' remains.
According to our correspondent, that process is currently being delayed by a rift between Thailand's chief pathologist and the police.
The police want to take control of the forensic investigation, but the medical adviser maintains that vital information will be lost if the bodies are moved, our correspondent adds.
In the town of Takua Pa, near the devastated Khao Lak resort, hundreds of Thai demonstrators protested outside the building where the Nordic leaders were meeting, to highlight another dispute involving the identification of bodies.
Holding photos of missing loved ones, the demonstrators complained about the government's plan to move bodies to a central location in Phuket - where they could be identified with more modern equipment.
They said it was difficult to travel to Phuket and that their plight was being ignored.
"I don't even have enough to eat," said Kulai Sirisuk, who lost her 4-year-old daughter.
"I certainly don't have enough money to travel to Phuket, and to recover the body of my daughter," she told the Associated Press news agency.