A North Korean defector-turned-spy was sentenced to four years in prison for attempting to kill a fellow defector in South Korea at the order of the communist regime, court officials said Thursday.

The secret agent, surnamed Ahn, was charged with plotting to kill Park Sang-hak, a defector leading anti-Pyongyang propaganda activities in the South, with a poisoned needle in September.

He was also ordered to pay 11.75 million won (US$10,399) in fines, the equivalent of his payment from the North.

"Severe punishment is needed for crimes that can threaten the existence and safety of the Republic of Korea (South Korea)," the Seoul Central District Court said in a ruling. "However, (the

court) took into consideration the circumstances that led Ahn to commit the crime, such as the fact that he was unexpectedly given the poisoned needle while gathering North Korea intelligence for the National Intelligence Service (NIS)," the South's spy agency.

Ahn defected to the South in 1995 and served as a director of a company handling inter-Korean economic projects. In 2010, he came into contact with a North Korean spy during business trips to Mongolia, and was later ordered to carry out the assassination, court officials said.

Ahn said he followed the instructions out of resentment for the NIS, as he informed the agency of the assassination plot and offered to gather top intelligence on the communist regime, but was rebuffed and even warned of possible legal consequences, according to the officials.

North Korea has said it opposes all forms of terrorism, though it has a track record of terrorist attacks against South Korea. The Koreas are technically at war with each other after the 1950-53 Korean War ended in a truce. (Yonhap News)