The number of North Koreans slipping illegally into Thailand has surged in recent months, according to immigration bureau officials, as tensions mount on the Korean peninsula because of Pyongyang's weapons programmes.

Thailand is on a popular transit route for North Koreans defecting from the impoverished communist state. Hundreds flee each year to China and make it to Thailand after an overland journey, from where they are usually sent on to South Korea.

In 2016, there were 535 North Korean arrivals in Thailand, but the first six months of this year saw 385 arrivals, according to data from Thailand's immigration bureau seen by Reuters, and more are arriving each week.

"An average of 20 to 30 North Koreans arrive each week now in northern Thailand alone," said an immigration official who spoke to Reuters on condition of anonymity.

The surge has come despite tighter controls by North Korea on its border with China. It coincides with rising tensions on the Korean peninsula over Pyongyang's stepped up nuclear and missile tests and warnings by the United States that it was losing patience with the isolated state.

However, Citizens' Alliance for North Korean Human Rights, a Seoul-based NGO, said the number of North Korean defectors coming to South Korea had not increased this year, implying that those coming through Thailand could be making up a higher proportion of the total.

The South's Unification Ministry said 593 North Korean defectors had come to the South in the first six months, against 1,418 last year and 1,275 in 2015.

Most North Koreans enter Thailand at its northernmost tip, near the Golden Triangle, from neighbouring Laos, the Thai immigration officials said, but new routes had also emerged further south.

"We have seen many North Koreans entering the country in several northeastern provinces along the Mekong River in the last few years," said Captain Chonlathai Rattanaruang, a commander of the Mekong River Navy patrol.

Another officer confirmed the trend. He told Reuters that groups of North Koreans have been entering Thailand through northeastern provinces bordering Laos including Nong Khai and Nakhon Phanom, where the Mekong forms the international frontier.


UNOFFICIAL UNDERSTANDING

Officially, Thailand treats North Koreans who enter the country as illegal migrants rather than refugees.

Thailand has not signed the 1951 Geneva Convention on Refugees and has no specific law on refugees.

Unofficially, arrangements are often made between Thai authorities, the South Korean government, and defectors on the ground.

"The North Koreans come to Thailand to get arrested so they will get an asylum to South Korea," said Roongroj Tannawut, a district official of Chiang Khong district near the Golden Triangle.

North Korean defectors who enter Thailand are arrested and prosecuted for illegal entry.

They are then transferred to an immigration detention centre in Bangkok before being deported, usually to South Korea.

"Since the South Korean constitution recognises all Koreans as its citizens, it is possible for Thailand to recognise South Korea as a legitimate destination to deport North Koreans," Phil Robertson, deputy director of Human Rights Watch's Asia Division, told Reuters.

The United Nations High Commissioner for Refugees rarely processes North Korean defectors in Thailand because of the arrangement between Thailand and South Korea.

"People fleeing North Korea don't usually approach UNHCR offices as they have other ways of seeking safety," Vivian Tan, spokeswoman for UNHCR Asia, told Reuters.

The South Korean Embassy in Bangkok declined to comment on their role when contacted.