North Korean banknotes at a stamp and money collection market in Beijing. Great enthusiasm in old North Korean won notes rouse among the collectors after Pyongyang announced redenomination of its old currency in 2009. Korea Times file

South Korea's spy agency on Thursday alerted the public to overseas fraud schemes selling defunct North Korean money, taking advantage of the country's recent move to reach out to the international community.

The National Intelligence Service (NIS) said crime rings in China and Southeast Asia have secured massive amounts of old North Korean bills and attempted to sell them on the premise that their value will jump once North Korea denuclearizes and its economy develops.

Most of the bills were issued before the North's currency reforms in 2009 and are no longer is use, according to the NIS.

They are also offering the money 30 to 40 percent cheaper than the current prices, the NIS said.

A crime organization was caught selling 5 million won worth of such bills in Thailand, it said. A South Korean businessman in Thailand received an offer from a local person to buy 2 billion won worth of bills. Similar cases were reported in other countries, too, largely in Southeast Asia, the NIS said.

South Koreans are mostly negative about possessing North Korean money but chances are high that international crime rings have their eyes on Korean residents as targets, the NIS said.

The spy agency plans to post warnings on websites of South Korean diplomatic missions. (Yonhap)