BEIJING - Two Chinese sailors remain missing after their cargo ships were hijacked on Oct 5, Chinese Foreign Ministry spokesman Liu Weimin said at a news briefing on Monday.

Xinhua News Agency earlier cited Thai authorities saying that all 13 Chinese crewmen were dead, and searchers found the last body in nearby Chiang Khong District early on Monday.

However, Thai investigators later said two of the 13 bodies they recovered did not belong to Chinese sailors, correcting the death toll of Chinese sailors to 11 killed and two missing.

After further investigation, at least two bodies do not match the descriptions of Chinese sailors, said Sermsak Seesan, chief of Chiang Saen District and head of the joint investigation team of police, military and local authorities.

According to Xinhua, Thai authorities on Monday identified the killers as a drug ring on the Mekong River in north Thailand. Investigators suspect that a drug ring of Shan or Tai Yai - an ethnic group led by Nor Kham - on the Mekong River in north Thailand was responsible for the incident, said Sermsak.

Major General Prakarn Chonlayuth, commander of the Pa Muang Task Force, Thailand's border army, said he believes Nor Kham's drug gang killed the crew because they refused to pay the gang protection money.

Nor Kham, 40, wanted on arrest warrants of Thailand and Myanmar for drug trafficking, expanded his illegal activities a few years ago to collect protection money from Chinese-flagged cargo ships, Prakarn said.

China has urged countries to take effective measures to strengthen the protection of Chinese vessels and crews on the Mekong River. The Chinese Foreign Ministry and Southwest China's Yunnan province have started an emergency mechanism to deal with the follow-up work, according to Liu.

Beijing has ordered Chinese passengers and cargo vessels to suspend trips along the Mekong River.

On Oct 5, Thai border troops seized drugs on-board two Chinese-flagged ships, the Yu Xing 8 Hao and Hua Ping, after a gunfight with drug traffickers that lasted more than 30 minutes in Chiang Saen District, bordering Myanmar. One drug trafficker was reportedly killed, while the others are still at large.

Local authorities seized amphetamines worth 100 million baht ($3.22 million) from the boats, which were also carrying garlic, apples and fuel.

Police on Friday found the bodies of three of the Chinese crewmen, with their hands tied behind their backs. Nine more bodies were found on Saturday.

Xinhua, Zhao Shengnan and Guo Anfei contributed to this story.