Malaysian police said on Friday they will not release the body of the estranged half-brother of North Korean leader Kim Jong-un until they receive DNA samples from his next-of-kin.

Police are investigating the death of Kim Jong-nam, the eldest son of the late North Korean leader Kim Jong-il.

Kim, 46, died on Monday after being assaulted at Kuala Lumpur International Airport with what was thought to be a fast-acting poison.

Two female suspects, one an Indonesian and the other carrying Vietnamese travel documents, have been arrested. A Malaysian man has also been detained to help with inquiries.

Police are still hunting four men believed to have been accomplices in the attack.

South Korea's spy agency told lawmakers in Seoul that it believed North Korean agents had killed Kim, acting on orders from North Korea's leader Kim Jong-un. U.S. officials told Reuters they also believed North Korean agents were responsible.

Malaysia North Korea

A suspect in the death of Kim Jong-nam — believed to be the woman in yellow, fourth from the left — is escorted by Malaysian officials to a vehicle in Kuala Lumpur on Thursday. (CCTV/Associated Press)

Under Chinese protection

The North Korean embassy officially requested on Thursday, for the body of Kim Jong-nam to be released by Malaysia, having earlier tried in vain to persuade Malaysian authorities not to carry out an autopsy.

Selangor state police chief Abdul Samah Mat told Reuters the body would not be released until next-of-kin DNA had been obtained to confirm the identity of the victim.

"We are still waiting for the next of kin application, we have not received it yet. We have only received the application from the North Korean embassy yesterday," the police chief  said. "We need to collect DNA samples from the next-of-kin in order to get conclusive evidence on the victim's identity."

Kim Jong-un

North Korean leader Kim Jong-un, seen here in an undated photo, is suspected by South Korea's spy agency and others of having ordered the killing of his estranged half-brother. (KCNA/Reuters)

North Korea has made no public reference to Kim Jong-nam's death, and calls to the embassy in Malaysia were unanswered.

Kim Jong-nam had spoken out publicly against his family's dynastic control of the isolated, nuclear-armed North Korea.

South Korea's intelligence agency told lawmakers in Seoul that Kim had been living with his second wife in the Chinese territory of Macau, where he received China's protection.

He had been at the airport to catch a flight to Macau when he was killed.

Cornelia Charito Siricord, director of forensics within the science ministry, told Reuters that an analysis was being carried out on samples taken from the body to help the police establish the cause of death.