A gang leader accused of masterminding the murder of 13 Chinese sailors on the Mekong River last year has pleaded guilty at a trial in southwest China, state media said Saturday.

The trial of Naw Kham, leader of a gang based in Myanmar's northern Shan state, and five of its other members, ended on Friday at a court in Kunming city, the official Xinhua news agency said.

The sailors were killed last October in a raid on two Chinese cargo boats on the Mekong, an attack thought to have been carried out by a notorious gang in the "Golden Triangle", an area known for drug production and smuggling.

Chinese prosecutors had accused the six suspects of intentional homicide, drug trafficking, kidnapping and hijacking, Xinhua said. The suspects, all foreign nationals, were taken to China in May this year.

All six pleaded guilty, although the gang leader originally claimed he was innocent at the start of the trial, which began on Thursday, Xinhua said. The court will announce sentences at a later date.

The Kunming Intermediate People's Court, where the trial took place, could not be reached for comment on Saturday.

Last year's incident sparked an angry reaction from China, which summoned diplomatic envoys from Thailand, Laos and Myanmar and asked authorities to speed up investigations into the incident.

The report quoted Nie Tao, a Chinese police officer investigating the murders, as saying nine soldiers from Thailand were involved in the case and Thai police were now investigating. It did not say how they were involved.

Chinese state media has said that the gang had more than 100 members and was suspected of kidnap, murder, looting and other crimes along the Mekong River, as well as drug smuggling.

Following the killings China and its Southeast Asian neighbours started armed patrols to protect ships navigating the Mekong River, a key waterway that flows through Yunnan province in China's southwest and into Southeast Asia.

China, Laos, Myanmar and Thailand on Friday launched their sixth round of patrols since December last year, the China Daily newspaper said Saturday.