South Korea's government says it's convinced the North Korean regime orchestrated the bizarre poisoning death of Kim Jong Nam, the estranged half-brother of North Korean leader Kim Jong Un.

"We are observing this pointless and merciless incident with grave concern," the South Korean Unification Ministry said in a statement Sunday.

The incident, which South Koreans are calling an assassination, happened last week at the Kuala Lumpur International Airport. Two women of Southeast Asian nationalities approached Kim and appeared to apply a liquid to his face and cover it with a cloth, authorities say. Shortly thereafter, Kim fell ill and sought help. He died before reaching the hospital.

The two women, a taxi driver and a separate suspect, are in Malaysian police custody. But Malaysian investigators say they identified an additional four men — all North Korean — as suspects in the crime. Investigators say those four men flew out of Malaysia on the day of the poisoning.

As the investigation continues, so does a diplomatic row over the late Kim's body. Malaysian authorities have conducted at least one autopsy, and authorities said the results will be released in the coming days.

North Korea's ambassador to Malaysia, Kang Chol, gave a statement to reporters outside the hospital morgue Friday, in which he said North Korea would "categorically reject" results of the autopsy because North Korean officials were excluded, and accused the Malaysians of working with "hostile forces" on the case.

Malaysian authorities said Sunday they are cooperating with Interpol in the investigation. They say they would release the body to the next of kin, but so far, Kim's next of kin have not come forward.

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