Police have strengthened security for a North Korean defector who serves as a ranking official at a South Korean state-run think tank after the North ordered his assassination, a source said Friday.

Since mid-January, police have beefed up the guard over Ko Young-hwan, vice president of the Institute for National Security Strategy, as North Korea is believed to have issued an order to kill him according to a source familiar with North Korean affairs.

Ko defected to South Korea in 1991 after serving as a North Korean diplomat at the North's embassy in the Congo.

Police raised the number of armed guards assigned to him after South Korea's spy agency obtained the intelligence.

South Korea said Thursday North Korean leader Kim Jong-un has ordered greater preparations for terror attacks on the South, including cyberattacks.

The North's Reconnaissance General Bureau, tasked with intelligence operations, is prepared for such disruptive acts, including terrorist attacks using poison or kidnapping South Koreans, it said.

Seoul said that the North may target anti-North Korean activists, defectors and Seoul government officials with its potential terror attacks. (Yonhap)