Drugs worth more than 2.5 billion yuan ($400 million) have been seized in a two-month multinational operation targeting crime along the Mekong River, China's drug enforcement chief said Tuesday.

From late April to late June, authorities from China, Laos, Myanmar and Thailand shared intelligence and hunted for drug lords and fugitives, resulting in the detention of 2,534 suspects and the seizure of almost 10 tons of drugs and more than $3.6 million in drug-related assets, according to Liu Yuejin, director general of the Narcotics Control Bureau of the Ministry of Public Security.

The four countries began joint security patrols along the Mekong River in late 2011 after the grisly murders of 13 Chinese sailors on a section of the river that flows through the Golden Triangle region, notorious for drug production and trafficking as well as extortion gangs. In March of this year, China executed the accused ringleader, Myanmar citizen Naw Kham, and three accomplices who were found guilty of the murders.

Liu told a news conference also attended by representatives from Laos, Myanmar and Thailand that following the trial and execution of Naw Kham, they had seen a "dramatic decline" in the activities of drug rings and criminals operating in the Mekong region and Golden Triangle. Their success has been seen in tighter supplies and higher prices for drugs in China and Thailand, he said.

"This shows that the demand for drugs has far exceeded the supply of drugs. This is because criminal rings and individuals during that time were afraid of carrying out high-profile activities," he said.

Liu said 60 to 70 percent of the drugs in China come from the Golden Triangle, where methamphetamine production is surging even as that of opium and heroin has been suppressed through enforcement efforts.

Liu said that in the future, the four countries would work toward poppy eradication in the Golden Triangle, northern Laos and northern Myanmar and promote the growing of substitution crops.