(Yonhap)
Kim was killed in an airport in Malaysia on Feb. 13 with toxic chemicals identified as VX nerve agent, which is listed as chemical weapon, Malaysian police said, citing a preliminary toxicology analysis.

"It will be better for North Korea to admit its assassination (of Kim Jong-nam) and cooperate with the probe," Jeong Joon-hee, a unification ministry spokesman, said at a regular press briefing.

"North Korea will see its international image further worsen (if it continues to deny the allegation)," he added.

Kim Jong-nam, the first son of late former leader Kim Jong-il, was killed last week after two Asian women allegedly wiped a toxic substance on his face. He was at the airport to await a flight to Macau to return home.

Malaysian police said that eight North Koreans are suspected of being involved in Kim's murder, along with the two women.

Four North Korean men fled Malaysia on the day of Kim's death and are now believed to have escaped to Pyongyang. Police arrested a North Korean man while looking for three others including a diplomat and an employee at Air Koryo, the North's flag carrier.

South Korea said that it is highly likely that Pyongyang is behind the murder, given its track record of committing terrorist attacks and inhumane acts.

North Korean leader Kim Jong-un issued a standing order to kill his brother after assuming power in late 2011, Seoul's spy agency said. (Yonhap)

South Korea on Friday called on North Korea to acknowledge that it is behind the killing of its leader's half-brother and cooperate with Malaysia's probe into the case. In its first official response to the death of Kim Jong-nam, North Korea blamed Malaysia for colluding with South Korea in its investigation while accusing Seoul of generating an anti-Pyongyang conspiracy.