The principal suspect for the murders of 13 Chinese sailors on the Mekong River last year denied plotting the attack on Thursday, when he and five other people went on trial in Southwest China for the crime.

During the trial that opened Thursday at the Intermediate People's Court of Kunming, capital of Yunnan Province, Naw Kham, the head of an armed drug gang from Myanmar, claimed he neither planned nor commanded the deadly attack in October 2011.

The six suspects, all foreigners or stateless people, have been charged with intentional homicide, drug trafficking, kidnapping and ship hijacking.

Naw Kham, who had confessed to the murders in an arranged interview with media before the trial, made a U-turn in court, saying he was not fully informed by his fellow ring members of the attack.

"I did not know about it at that time," he told the court. "They did not tell me. I was only informed afterward."

Naw Kham did admit that he was the gang's ringleader, saying every member called him "the boss."

One witness at the court said Naw Kham, dubbed "Godfather" for running one of the most notorious armed drug rings on the section of the Mekong River near the China-Myanmar-Laos borders, maintained an unperturbed smile during the morning's proceedings.

All of the six accused appeared before the court on Thursday. The trial is expected to last for three days.

According to the bill of indictment presented by prosecutors, a large amount of evidence, including DNA test results, autopsy reports and witness testimonies, will be produced before the court during the trial.

Present at the court were relatives of the 13 Chinese victims, embassy personnel of the related countries, Chinese legislators, political advisors, experts and representatives of local residents and media.

Simultaneous translations of comments and material into the national languages of the suspects were provided in court.

The crime ring was busted earlier this year in a joint operation by police from China, Laos, Myanmar and Thailand after the brutal murders of Chinese sailors triggered an outcry in China last year.

A previous police investigation found that Naw Kham, core members of the gang and a small number of Thai soldiers attacked, hijacked and finally murdered 13 Chinese sailors on two cargo ships, the Hua Ping and Yu Xing 8, on Oct. 5, 2011, near a port in Thailand on the Mekong River.

Naw Kham was sent to China via a chartered plane in May.

"It is uncommon in China's judicial practice for foreigners who commit crimes against Chinese nationals outside China to be brought to justice before a Chinese court," Dong Lin, vice president of the Intermediate People's Court of Kunming City, told media before the trial.

Li Ruokun, deputy procurator of the Yunnan Provincial People's Procuratorate, said the trial showed China's resolution to severely punish cross-border crimes and to protect the legitimate rights of its citizens.

Li said the suspects' rights were fully respected.

Lin Li, Naw Kham's lawyer, said her rights to meet the defendant and access his criminal files were guaranteed.

With a length of almost 5,000 km, the Mekong River, known in China as the Lancang River, is one of the most important waterways in southeast Asia, linking the countries of China, Laos, Myanmar and Thailand. It plays a crucial economic role among the Greater Mekong Sub-region countries.