The killing of North Korean leader Kim Jong-un's half brother is a terrorist act that revealed Pyongyang's brutality, South Korea's unification ministry said Monday.

"We could clearly understand the latest incident reaffirmed the unpredictability and brutality of the North Korean regime," Jeong Joon-hee, a ministry spokesman, told a press briefing.
Unification Ministry spokesman Jeong Joon-hee (Yonhap)
On Sunday, the ministry said that it believes the North Korean regime is behind the murder of Kim Jong-nam as some of suspects were identified as North Korean nationals.

The spokesman said Sunday that Seoul is closely watching the latest "reckless and horrible" incident with grave concern, given North Korea's record of involvement in terrorist acts and crimes against humanity.

Acting President and Prime Minister Hwang Kyo-ahn called on government officials on Monday to seek international cooperation to make North Korea "pay a due price for its terrorist act."

Jeong declined to comment on what consequences Pyongyang would face, but raised the need to stay alert against North Korea's possible security threats, citing its latest test of a new ballistic missile.

Kim Jong-nam, the eldest son of late former leader Kim Jong-il, was killed at an airport in Malaysia Monday after two Asian women sprayed an unidentified poisonous substance on his face. He was at the airport for a flight to Macau to return home.

Malaysian police said Sunday that at least five North Korean suspects appeared to be involved in Kim's death. (Yonhap)

Police arrested Ri Jong-chol, a 46-year-old North Korean man, on Friday night following the arrest of three others including the two Asian women. They said they are looking for four more North Koreans who fled Malaysia on the day of Kim's death. (Yonhap)