A North Korean defector allegedly armed with poison needles has been arrested on suspicion of plotting to attack a leading activist, South Korean officials said.
They said that a defector surnamed Ahn planned to target Park Sang-hak, another North Korean defector who leads a campaign that sends leaflets attacking Pyongyang's leaders to the North.
Authorities said they foiled the attack. A National Intelligence Service official said Ahn was carrying poison needles when he was arrested.
The investigators did not immediately link the latest case to North Korea and would not comment on local media speculation that Ahn might be an infiltrator similar to one jailed earlier this year.
In the previous case, a South Korean court sentenced a North Korean agent to 10 years in prison for plotting to assassinate Hwang Jang-yop, a high-profile defector and former senior member of the North's ruling party.
The agent had come south posing as a defector, but his identity was discovered during an interrogation.
If charged under the South's National Security Law, Ahn could face the death penalty.
More than 21,000 North Koreans have defected to the South since the 1950-53 Korean war ended with a truce.