Kim Jong-nam, the eldest son of late former leader Kim Jong-il, was killed at an airport in Malaysia last Monday after two Asian women sprayed an unidentified poisonous substance in 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.

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.

South Korea's unification ministry said Sunday that it believes the North Korean regime is behind the murder of Kim as the five suspects are North Korean nationals.

The ministry said 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.

"It is highly likely that the North Korean regime is behind the assassination," Unification Minister Hong Yong-pyo told foreign correspondents in Seoul on Monday.

"The whole world has already regarded the North Korean regime with suspicion from the very beginning of this incident."

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

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

"We could clearly understand the latest incident reaffirmed the unpredictability and brutality of the North Korean regime," Jeong told a press briefing Monday.

Malaysia's foreign ministry recalled its top envoy to Pyongyang and summoned North Korea's Ambassador to Kuala Lumpur Kang Chol on Monday in connection with Kim's death.  

Following the closed-door meeting with Malaysian officials, Kang told reporters that North Korea "cannot trust the investigation by the Malaysian police.

The diplomat accused the police investigation of being politically driven, demanding that Malaysia allow a joint probe into the murder with the North Korean government.

He also claimed that South Korea conspired with the Malaysian government to lay the blame on Pyongyang.

Kang said Friday that North Korea won't accept the result of the autopsy as it was performed without Pyongyang officials in attendance.

He demanded that Malaysia immediately hand over his body, accusing Malaysia of trying to deceive Pyongyang and colluding with what he calls "hostile forces" to do the North harm.

Malaysian police said Sunday they would give two weeks to Kim's next of kin to claim his body. (Yonhap)