(CNN) -- At least 12 Chinese sailors have been killed after their cargo ships were attacked on the Mekong River in the northern Thai province of Chiang Rai, the Chinese Foreign Ministry in Yunnan Province has said.





The ministry's website stated that two Chinese cargo ships -- the Hua Ping and Yu Xing 8 -- were attacked with gunfire on October 5. According to the initial investigation, all six sailors from Hua Ping and six of the seven sailors from Yu Xing 8 were found dead, while one remained missing.





Though still in the early stages of their investigation, Thai police say they cannot rule out the involvement of drug gangs in the killings.





Chiang Rai police colonel Popkorn Khuncharoensuk told CNN that the two ships were raided by a joint task force of army, marine police, local police and paramilitary following the attack, and found almost one million amphetamines on the vessels.





"This is the most gruesome incident I have ever seen," Popkorn said.





According to Popkorn, one of the bodies was found aboard the Hua Ping, while the rest were found in the Mekong River near Chiangsaen port. Three of the bodies remained unidentified, and some were found with their hands cuffed or tied.





"I can't rule out all possibilities, but initially there appears to be drugs involved," Popkorn said. "But we can't just quickly jump to the conclusion that it was carried out by drug gangs. The case is complicated, and we have to be very thorough."





The violent incident has unnerved many of those who ply their trade on the river.





"There are no cargo ships leaving or coming to Chiangsaen port," said Surachart Janthawatcharakorn, Chief of Chiangsaen Customs Office. "They have all halted their traveling because they are still frightened by the incident, and are still very concerned about their safety."





The Chinese Foreign Ministry said the Chinese Embassy in Thailand and its consulate general in Chiang Mai were investigating the murders and were working closely with Thai authorities and other relevant countries to hunt down the criminals.





CNN's Kocha Olarn and Haolan Hong contributed to this report.
When did it happen? How many ships were attacked? Where were the ships from? Who is China working with? Where were two Chinese ships attacked? Who were killed? Who was killed? How many sailors were killed?
October 5. two Chinese Thai authorities and other relevant countries on the Mekong 12 Chinese sailors 12 Chinese sailors 12
question: When did it happen?, answer: October 5. | question: How many ships were attacked?, answer: two | question: Where were the ships from?, answer: Chinese | question: Who is China working with?, answer: Thai authorities and other relevant countries | question: Where were two Chinese ships attacked?, answer: on the Mekong | question: Who were killed?, answer: 12 Chinese sailors | question: Who was killed?, answer: 12 Chinese sailors | question: How many sailors were killed?, answer: 12