Malaysia has sought Interpol to put up an alert to apprehend four North Korean suspects who fled in the murder of Kim Jong Nam, Malaysia's chief police officer Khalid Abu Bakar said on Thursday. The estranged half-brother of North Korean leader Kim Jong Un was killed in Kuala Lumpur's main airport last week.

South Korean and U.S. officials called the murder an assassination carried out by North Korean agents, said Channel NewsAsia. Police are currently holding one North Korean man under custody, but are still searching for another seven who are alleged to be connected to the murder.

Three of them, reportedly a diplomat, a state airline official, and another man, are believed to still be in Malaysia. The other four are believed to have made their way back to North Korea on the day of the murder, Feb. 13.

Khalid revealed on Thursday that two women of different nationalities - one Vietnamese and one Indonesian, were arrested last week over the suspicion of carrying out a fatal assault on the North Korean using a fast-acting poison. The two suspects, however, declined to admit if they were working for a spy agency.

Khalid told reporters, "If you have nothing to hide, you should not be afraid to cooperate, you should cooperate." He referred the statement to the police's action of sending an official request to the North Korean embassy, seeking to interview the embassy's second secretary and the airline official.

Having released their names on Wednesday, Khalid explained that an arrest warrant will not be issued for the second secretary, considering his possession of diplomatic immunity in North Korea. However, he insisted that "the process of the law will take place" if the airline official does not come forward.

Khalid also denied that Malaysian police officers had been sent to Macau, where Kim Jong Nam and his family had been living under Beijing's protection, according to Reuters. Meanwhile, North Korea's ambassador said the Malaysian investigation is not trustable, and issued a statement on Wednesday compelling the three detained suspects to be released soon.