Malaysian police have announced the arrest of a fourth suspect, a North Korean, over the death of the half-brother of the North Korean leader.

The man identified as Ri Jong Chol was arrested on Friday in Selangor near Kuala Lumpur, police said, giving no other details.

Two women, one of them Indonesian and the other travelling on a Vietnamese passport, and a boyfriend of one of them, had been arrested earlier on suspicion of involvement in the death of Kim Jong Nam.

South Korea has accused its enemies in North Korea of sending a hit squad to kill Kim Jong Nam at the airport in Kuala Lumpur, saying two female assassins poisoned him and then fled in a taxi.

Meanwhile, a second post-mortem will be carried out on Kim Jong Ham after a senior Malaysian official said the result of the first one was inconclusive.

Earlier, North Korean Ambassador Kang Chol said Malaysia conducted the first post-mortem "unilaterally and excluding our attendance" and warned that his government will reject any findings.

Indonesia's police chief has said the Indonesian woman arrested for suspected involvement in the death was duped into thinking she was part of a comedy show prank.

Kim Jong Nam, who was 45 or 46 and had lived in exile for years, suddenly fell ill at the Kuala Lumpur airport on Monday as he waited for a flight home to Macau.

Dizzy and in pain, he told medical workers at the airport he had been sprayed with a chemical. He died while being taken to a hospital.

"We will categorically reject the result of the post-mortem," Mr Kang said, adding that the move disregarded "elementary international laws and consular laws".

He said the fact Malaysia has yet to hand over the body "strongly suggests that the Malaysian side is trying to conceal something which needs more time and deceive us, and that they are colluding with the hostile forces towards us who are desperate to harm us".

Indonesian police chief Tito Karnavian, citing information received from Malaysian authorities, said Siti Aisyah, 25, was paid to be involved in "Just For Laughs" style pranks, a reference to a popular hidden camera show.

He said she and another woman performed stunts which involved convincing men to close their eyes and then spraying them with water.

"Such an action was done three or four times and they were given a few dollars for it, and with the last target, Kim Jong Nam, allegedly there were dangerous materials in the sprayer," Mr Karnavian said.

"She was not aware that it was an assassination attempt by alleged foreign agents."

His comments come after a male relative of Aisyah said in an Indonesian television interview that she had been hired to perform in a short comedy movie and travelled to China as part of this work.

Indonesian Immigration has said Aisyah travelled to Malaysia and other countries it did not specify.

Investigators were still trying to piece together details of the case, and South Korea has not said how it concluded that North Korea was behind the killing.

Malaysian police were questioning Aisyah, another woman who carried a Vietnamese passport, and a man they said is Aisyah's boyfriend.

Kim Jong Nam was estranged from his younger half-brother, the North Korean leader Kim Jong Un.

He reportedly fell out of favour with their father, the late Kim Jong Il, in 2001, when he was caught trying to enter Japan on a false passport to visit Tokyo Disneyland.

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