China urged calm and restraint on Wednesday after South Korea called for the possible suspension of North Korea's seat at the United Nations to punish it for using chemical weapons to kill the half-brother of its leader.

Malaysian police have said two women smeared VX nerve agent, a chemical on a United Nations list of banned weapons of mass destruction, on Kim Jong Nam's face in an assault captured on security cameras in the Malaysian capital's airport on February 13.

U.S. and South Korean officials believe Kim Jong Nam was the victim of an assassination orchestrated by North Korea.

North Korea said on Tuesday it "categorically rejects" what it called "fictitious and preposterous assumptions".

Speaking at the U.N.-backed Conference on Disarmament in Geneva on Tuesday, South Korea's Foreign Minister Yun Byung-se said the use of chemical weapons was a "wake-up call" and the international community should act - including possibly suspending the isolated North's seat at the United Nations.

"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 United Nations.

"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," Geng told a daily news briefing, without elaborating.

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

However, China has pushed for talks to resolve the stand-off, and this week is playing host to a senior North Korean diplomat, Vice Foreign Minister Ri Kil Song, the first such high-level visit since June.

Ri is scheduled to meet Chinese Foreign Minister Wang Yi.

Under the Chemical Weapons Convention, the Organisation for the Prohibition of Chemical Weapons states parties can "in cases of particular gravity" bring an issue to the attention of the U.N. Security Council and the U.N. General Assembly. 

The U.N. Security Council can recommend to the 193-member General Assembly – likely through the adoption of a resolution - that a state be suspended or expelled. Such a move would need to be approved by two-thirds majority of the General Assembly.

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, North Korean leader Kim Jong Un.