Malaysia is considering expelling North Korea's envoy to the Southeast Asian nation or shutting its embassy in Pyongyang, as tensions escalate over the killing of the estranged half-brother of the North's leader Kim Jong Un, a senior government official said.

Kim Jong Nam, 46, was killed at Kuala Lumpur International Airport on Feb. 13 with what police believe was a fast-acting poison, as he prepared to board a flight to Macau where he lived in exile with his family under the protection of Beijing.

North Korea's ambassador said last week his country "cannot trust" Malaysia's handling of the probe, and also accused the country of "colluding with outside forces" - a veiled reference to bitter rival South Korea.

A senior Malaysian government official who is familiar with the discussions said Ambassador Kang Chol's comments have angered Malaysia and it was preparing a response, which could including declaring the ambassador "persona non grata".

Such a move would be the strongest response Malaysia could take against a foreign diplomat, and would mean Kang Chol would have to leave the country.

The source said Malaysia was also considering other options. The country, which has until now been one of the few nations to maintain friendly ties with the isolated North, could close its embassy in Pyongyang, or end visa-free travel for North Koreans entering Malaysia.

If the criticism from North Korea did not stop, all diplomatic and trade ties could be cut, the source added.

The Malaysian foreign ministry did not answer phone calls seeking comment.

Malaysian Prime Minister Najib Razak said earlier his week that the ambassador's comments casting doubt over Malaysia's investigation were "diplomatically rude".

"The statement by the ambassador was totally uncalled for ... But Malaysia will stand firm," Najib told reporters on Tuesday.

"CROSSED THE LINE"

Malaysia is among the few foreign countries that North Koreans can travel to easily, thanks to a visa-free policy for visitors that is largely reciprocated by Pyongyang.

Since the 1980s, North Korea has used the Southeast Asian nation as a hub to promote its strategic and business interests, legitimate and otherwise, some analysts say.

But the tensions with Malaysia may further isolate North Korea.

Pyongyang's nuclear arms and weapons programmes have alarmed the West, most recently its test of a ballistic missile earlier this month in its first direct challenge to the international community since Donald Trump became U.S. president.

Malaysian police on Wednesday named a North Korean diplomat and a state airline official who they said were wanted for questioning over the killing of Kim Jong Nam.

In all, police say they have identified eight North Korean men, one Vietnamese woman and one Indonesian women in connection with the killing. They said at least four of the suspects have fled the country and are most likely in Pyongyang.

North Korea has not responded to Malaysia's allegations of the possible involvement of its diplomat in the case. Attempts by Reuters to contact the North Korean embassy by phone were unsuccessful, and reporters were not allowed to enter the embassy to seek comment.

South Korean and U.S. officials believe the killing of the elder half-brother of Kim Jong Un was an assassination carried out by agents of the North.

North Korean diplomats spent hours last week trying to talk Malaysian officials out of conducting an autopsy on Kim Jong Nam's body, sources familiar with the discussions told Reuters, but Malaysia rejected the requests.

The body is still at a hospital in Kuala Lumpur, as the autopsy has yet to be completed.

On Thursday, Malaysian Defence Minister Hishammuddin Hussein said that the North's ambassador had breached diplomatic norms with his comments.

"He crossed the line. To me, this is a diplomatic irregularity," he was quoted as saying in The New Strait Times.