Two North Korean spies have been arrested while plotting to murder a high-ranking North Korean defector, the prosecution here said Tuesday.

The North Koreans -- only identified by their family names Kim and Tong -- are accused of attempting to assassinate, under the order of the spy agency belonging to the North's Ministry of People's Armed Forces, the Seoul Central District Prosecution said, according to Yonhap news agency.

Hwang defected to South Korea in 1997, and has been under constant threat of his life as he has persistently campaigned for the collapse of the Kim Joing-il regime. In the latest threat, Uriminzokkiri, the official Web site of a North Korean reunification organ, said early this month the 88-year-old is "an ugly traitor" and warned he "will never be safe."

The North Korean spies secretly entered Thailand via the Chinese city of Yanji last December with an order to kill Hwang while disguising themselves as defectors. Later, they were forcibly sent to South Korea, according to the prosecution.