North Korea said on Wednesday the claim that VX nerve agent was used to kill one of its citizens in Malaysia was "absurd" and lacked scientific basis.

Last week, Malaysian police said VX, a chemical classified by the United Nations as a weapon of mass destruction, was used to kill Kim Jong-nam, the estranged half-brother of North Korean leader Kim Jong-un, on February 13.

South Korean and US officials have said they believe North Korean agents orchestrated Kim's assassination. North Korea responded by saying the accusations were made to tarnish Pyongyang's image.

North Korea's state-run news agency on Wednesday said the claim that small amounts of the extremely toxic nerve agent were detected in the corpse was an "absurdity" lacking "scientific accuracy and logical coherence".

The Korean Central News Agency report came as two young women accused of actually carrying out the attack in a crowded airport were charged with murder.

Indonesian Siti Aisyah, 25, and Doan Thi Huong, 28, from Vietnam, were surrounded by a heavy police presence as they were charged in a Kuala Lumpur court.

The handcuffed women wearing body armour were both told they faced the death penalty if found guilty.

Malaysian police say they are also searching for several North Korean suspects.

North Korea has repeatedly criticised Malaysia's investigation and has not acknowledged the victim's identity. A high-level delegation from Pyongyang is in Malaysia demanding a return of the body and the release of a North Korean suspect being held.

Meanwhile, China urged calm and restraint on Wednesday after South Korea called for the possible suspension of North Korea's seat at the UN to punish it for allegedly using chemical weapons to kill Kim Jong-un.

"What I need to say is that the situation at present on the Korean peninsula is complex and sensitive," Chinese Foreign Ministry spokesman Geng Shuang said, when asked whether North Korea should be suspended from the UN.

"In this situation, we hope all sides can maintain calm and exercise restraint and not do anything to irritate each other or that may raise regional tensions."

Court charges two women with Kim Jong-nam murder

While China is North Korea's most important remaining international supporter, it has been angered by North Korea's repeated missile and nuclear tests and has supported tough UN sanctions.

Kim Jong-nam had been living in exile, under Beijing's protection, in the Chinese territory of Macau, and had criticised the regime of his family and his half-brother.