South Korea foils plot to kill top North defector

SEOUL (Reuters) - South Korea has arrested two North Koreans it said were sent by Pyongyang to assassinate the highest-ranking North Korean official to defect to the capitalist state, the South's spy agency said Wednesday.

The arrest comes at a sensitive time in ties between the rival Koreas following the deadly sinking of a South Korean navy ship last month, which many in the South believe was likely torpedoed by the North.

The North Koreans' mission was allegedly to assassinate Hwang Jang-yop, 87, a former North Korean Workers' Party secretary and a key architect of the North's socialist ideology who has been harshly critical of leader Kim Jong-il since his defection 13 years ago.

Prosecutors in Seoul have indicted the pair for national security law violations and conspiracy to commit murder after uncovering the plot during routine interrogation given to North Korean refugees, a spy agency official said.

The pair entered the South early this year from Thailand, claiming refugee status. North Korean defectors almost always first cross into China and then seek entry into the South via a third country.

The pair of North Korean agents were told by Pyongyang to track the whereabouts of Hwang in the South while awaiting orders to assassinate him, the spy agency official said, asking for anonymity.

Hwang lives under heavy protection. Those close to him said that during his fiery anti-North speeches, he will not drink water provided to him on the podium out of concern that it could be poisoned.

(Reporting by Jack Kim; Editing by Jon Herskovitz and Alex Richardson)