Among the three South Korean drug smugglers who were executed in China recently, two were nabbed while trafficking North Korean opium in northeastern China’s Liaoning, Jilin and Heilongjiang provinces.

Park said in order to avoid detection by U.S. satellites, the North cultivates the poppies in many different areas along the border.

Dream Makers for North Korea, led by former lawmaker Park Sun-young that aids North Korean defectors, on Monday unveiled a picture of an opium poppy field in Hoeryong, North Hamgyong Province. The group says it was taken in July last year by a source in China who infiltrated North Korea.

Opium grown near North Korea's border with China is flooding the Northeast Chinese market, according to an activist group.

The raw opium is usually smuggled into the towns of Helong and Chiangbai in Jilin province to transport to the three northeastern provinces, because the two towns are located at the upper reaches of the Tumen and Yalu river, which are shallow points, making it easy for smugglers to cross.

A source in China said one reason why Chinese security forces have set up barbed wire fences along the two border towns and closely monitor North Koreans wading across the rivers is to crack down on drug smuggling.

Drug dealers on both sides of the border have forged close relationships, which allows for rapid distribution. North Korea's Workers Party operates an agency known as Room 39, which manages Kim Jong-un's illicit funds that is spearheading illegal activities, while the military and state security are also involved in drug production and distribution.

North Korean drug dealers fill broken LCD TVs with narcotics and send them to China under the pretense of having them repaired. They also pack them together with pungent kimchi to mask the smell of the drug.

Chinese drug dealers have so far mostly bought narcotics from the Golden Triangle, which covers jungle parts of Burma, Laos and Thailand. But North Korea has recently emerged as a new supplier.

The Chinese journal Legal Daily recently published an in-depth article on North Korean drugs and reported that the three Chinese provinces bordering the North have become "disaster zones" impacted by the illicit drug trade.

The North started opium poppy cultivation back in 1992. A Chinese military journal reported that the North produces around 40 tons of opium a year as well as some 3,000 kg of synthetic drug that generate US$100-200 million a year in revenues.

The North Korean towns of Chongjin and Heungnam are believed to house narcotics factories.

North Korea's Foreign Ministry flatly denied the allegations, claiming that production and distribution of illegal drugs is "strictly prohibited."