Two South Koreans arrested in Japan last fall on suspicion of violating the country's immigration law had been involved in an operation to obtain foreign currency under the direction of a man believed to be a North Korean agent, investigative sources said Thursday.

Japanese police have classified their cooperation as a spy case involving North Korea and believe it is just one part of a foreign currency acquisition network put in place by Pyongyang to circumvent economic sanctions.

According to the sources, the man who gave the orders to the South Korean pair via several other individuals mainly operated from China, using fictitious names such as Ri Ho Nam.