Junta leader and Prime Minister Prayuth Chan-ocha urged the media to warn tourists about travel safety in a country popular with Australian tourists, and appeared to call into question the behaviour of the victims found hacked to death on Koh Tao in the Gulf of Thailand.

Hannah Witheridge and David Miller, both 24, had attended a beach party before they were bludgeoned with a hoe and their near-naked bodies were found shortly after dawn on Monday in a rocky alcove.

Telling police to find the killer or killers swiftly, General Prayuth said: "We have to look into the behaviour of the other party too, because this kind of incident should not happen to anybody and it has affected our image.

"Local people must tell tourists when the safe times are to be outside, we have to help them understand," he said. "In their countries [foreigners] can travel wherever they want, so they thought it is safe, but in our country, there are still problems … there are different types of people, so they have to be careful."

Despite the imposition of martial law across the country following a coup in May, all-night parties on beaches like Koh Tao and neighbouring Koh Phangan have seen rapes, robberies, drug arrests and shakedowns, according to consular staff of foreign embassies in Bangkok.

Many of the crimes are not reported to police.

Larry Cunningham, Australia's recently retired honorary consul based in Phuket, has said that Australian parents would be shocked to know how Thai criminals target young Australians and other foreigners at parties like those on Koh Phangan, where each full moon up to 30,000 ravers cram into one kilometre of beach.

"They are some of the worst criminals in Thailand … rapists, murderers and thieves, and some are corrupt police," Mr Cunningham said. "These are dangerous, dangerous places."

General Prayuth made the comments despite a 10 per cent fall in tourist arrivals in the country, where tourism accounts for 10 per cent of the economy.

Martial law has kept many visitors away as they are unable to buy travel insurance for destinations where martial law is in place.

General Prayuth said there are no plans to lift martial law.

Since ousting Thailand's democratically-elected government following months of political unrest, the junta has moved to crack down on prostitution, sleaze, drugtaking and police extortion in resort areas.

On Phuket, an island where up to 20,000 Australians holiday each month, armed soldiers have supervised the removal of illegal beach structures, including restaurants, and targeted mafia-type gangs operating rip-off taxis and tourist scams.

Chatpong Chatphum, the governor of Surat Thani region, which includes the island of Koh Tao, said the murders had dealt a serious blow to tourism and that more security cameras would be installed on beaches.

Thai police appeared to be left without any suspects for the killings of Mr Miller and Ms Witheridge after they released six hotel workers from Myanmar after hours of interrogation on the island.

Police have obtained blurred security camera footage of an Asian-looking man walking back and forth near the crime, now their only apparent lead.

Police say Ms Witheridge appears to have been dragged alive about 15 metres after she was attacked by the killer or killers, who may have attempted to rape her. She was then bludgeoned to death with the hoe that was found near the bodies.

Photographs of the bodies have been circulating on the internet.

Mr Miller, a civil engineering student at Leeds University, had met Ms Witheridge while both were staying at the island's Ocean View Bungalows.

More than 70 police officers have been sent to the island, 410 kilometres south of Bangkok, a popular diving destination that is also called Turtle Island.

The bodies of Mr Miller and Ms Witheridge have now been taken to Bangkok for forensic examination.