Malaysia's Prime Minister Najib Razak said on Monday his government's investigation of the killing of the North Korean leader's half-brother, Kim Jong-nam, will be "objective" — while tensions between the countries rose and video emerged that appears to show the fatal attack. 

Earlier on Monday, Malaysia said it has recalled its envoy from Pyongyang and summoned North Korea's ambassador in Kuala Lumpur, who again cast doubt on the impartiality of Malaysia's investigation into the killing and said the victim was not Kim Jong-nam.

"We have no reason why we want to do something to paint North Korea in a bad light, but we will be objective," Najib told reporters in the Malaysian capital, Kuala Lumpur.

Surveillance footage obtained by Reuters appears to show Kim Jong-nam being attacked at Kuala Lumpur International Airport on Monday last week by a woman, who is believed to have wiped a fast-acting poison on his face.

Reuters could not independently verify the authenticity of the video, and police officials were not immediately available for comment.

Kim Jong-nam, 46, who had been living in the Chinese territory of Macau under Beijing's protection, had spoken out publicly against his family's dynastic control of isolated, nuclear-armed North Korea.

South Korean legislators last week cited their spy agency as saying the young and unpredictable North Korean leader, Kim Jong-un, had issued a "standing order" for his half-brother's assassination, and that there had been a failed attempt in 2012.

Malaysian police are hunting four North Koreans who fled from the country on the day of the attack, having already detained one North Korean man, a Vietnamese woman, an Indonesian woman and a Malaysian man.

At least three of the wanted North Koreans caught an Emirates flight to Dubai from Jakarta late on the day of the attack, an immigration official in Indonesia told Reuters.

Malaysia's Star newspaper reported that all four had returned to North Korea.

Malaysia's health minister said autopsy results could be released by Wednesday.

The country is one of the few that maintains ties with North Korea and the dispute could further isolate the impoverished reclusive state. 

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North Korean leader Kim Jong-un had a 'standing order' for his half-brother's assassination, South Korean legislators said last week, citing their spy agency. (Associated Press)

'Unforgivable and inhumane'

South Korean Prime Minister Hwang Kyo-ahn told a meeting of the country's National Security Council that North Korea was almost certainly behind the killing.

"The murder carried out in public at an international airport of a third country is an unforgivable and inhumane criminal act and clearly demonstrates the recklessness and brutality of the North Korean regime that will spare no avenues when it comes to perpetuating itself," Hwang said.

"The North Korean regime's terrorism tactics are getting bolder so we must be more vigilant."

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Airport surveillance video shows a woman — identified as the Vietnamese suspect, wearing a white shirt — approaching Kim Jong-nam from behind and seemingly throwing something over his face. (Reuters)

The grainy CCTV images showed Kim, wearing a light-coloured jacket and trousers and with a backpack on one shoulder, heading for an automatic check-in counter in the airport departure hall.

A woman approaches Kim from behind on the left and another — identified as the Vietnamese woman, wearing a white shirt — walks rapidly up behind him from his right, before what appears to be a scuffle takes place.

In footage taken from another angle, the woman in the white shirt appears to lunge from behind and throw something over his head, locking her arms around him briefly.

As the woman in white quickly walks away, the second woman also moves off rapidly in another direction.

Later footage shows the portly, balding middle-aged man stumbling, wiping his face, and seeking help from people while gesturing to his eyes before being escorted to a clinic.

China irritated 

The mother of the detained Indonesian woman told Reuters that her daughter, Siti Aishah, had been duped into believing she was part of a television show or advertisement.

According to Malaysian media, the Vietnamese suspect, Doan Thi Huong, told police she had been tricked into taking part in what she thought was a practical joke.

There is speculation that China's patience with North Korea could be tested by the killing because Kim had been living in Macau, where he was headed when he was attacked.

China said on Saturday it had suspended coal imports from the North, a vital source of revenue.

China is seen to be irritated by the North's repeated aggressive behaviour, including two nuclear tests since early 2016 and a Feb. 12 intermediate-range ballistic missile launch, the latest in a series of missile tests.