A soldier was killed when his boat capsized in a river in northeast Thailand.

Flight Sergeant First Class Sukkasem Promphanchai was on patrol in the Mekong River when his squad spotted a fertiliser sack believed to contain drugs on June 10.

The troops rowed their boat toward the patch of land some 500 metres (1,600 feet) from the riverbank but it overturned amid strong currents.

Sukkasem's two companions were able to swim their way back to shore, but he was reportedly swept away by the churning waters.

A joint search team of Navy officers, rescue divers, marine police, and Mekong Riverine Unit members were deployed to scour the river.

They found Sukkasem's corpse at 12:30 am today, June 12, around 20 metres (70 feet) from where he disappeared.

General Manus Chandee, the Thai army's chief of joint staff, said: 'His body was taken back to land and was sent to the Khemmarat Hospital. It will later be transferred to Sunpasitthiprasong Hospital for a post-mortem exam.'

Sukkasem's remains will then be handed over to the Air Force's Security Force Command in Bangkok for a funeral.

Sukkasem was killed in the Golden Triangle area, where most of Southeast Asia's meth supply comes from.

The notorious narcotics hub is found where the borders of Thailand, Laos, and Myanmar meet, but it has long been a feral nest of criminal activity, including opium production, meth labs and call centre scam bases.

At the heart of the Golden Triangle lies the Golden Triangle Special Economic Zone (GTSEZ), run by notorious Chinese business tycoon and suspected crime boss Zhao Wei in the Chinese vassal state Laos. Communist chiefs are said to turn a Nelsonian eye to his wrongdoing.

In 2007, Zhao brokered a deal with the Laos government and obtained a 99-year lease to build the zone on a 39-square mile patch of impoverished Bokeo province.

The Chinese businessman claims to be a benefactor as he touts the GTSEZ as a tourist and economic hub designed to bring more income and investments into the country. However, both local and international law enforcement agencies believe it is a front for organised crime, including human trafficking, drug trafficking, and call-centre scams.

International authorities have struggled to take down the gambling empire as the Laos government itself is said to be protecting the GTSEZ, in which it has a 20 per cent stake.