GENEVA (Reuters) - South Korea called on Tuesday for “collective measures” against North Korea, including possible suspension of its United Nations membership, saying the use of chemical weapons to assassinate the half-brother of North Korea’s leader was a “wake-up call”.

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Foreign Minister Yun Byung-se was addressing the U.N.-backed Conference on Disarmament (CD) after Malaysia’s attorney general said two women will be charged with the murder of Kim Jong Nam.

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

“Just a few grams of VX is sufficient for mass killing,” Yun told the Geneva forum, referring to the nerve agent that Malaysian police said was used.

“North Korea is reported to have not just grams but thousands of tonnes of chemical weapons including VX all over the country ... The recent assassination is a wake-up call to all of us to North Korea’s chemical weapons capability and its intent to actually use them,” Yun said.

States could invoke the Chemical Weapons Convention, as the use of such agents is in violation of international law, he said. Malaysia is part of the 1993 pact prohibiting their production, transfer and use, but North Korea is not.

Once the Malaysian government releases the results of its investigation, the U.N. Security Council and state parties to the Chemical Weapons Convention should take up the case as a “high priority”, he said.

States that have ratified the chemical weapons ban could invoke the treaty and “take collective measures”, Yun added.

“Now is the time, I believe, for us to seriously consider taking extraordinary measures in all relevant regional and international fora including the U.N. as well as the CD.”

“It could take the form of suspension of North Korea’s rights and privileges as a U.N. member,” he said, calling South Korea’s isolated neighbour a “serial rule-breaker”.

Yun, in a speech on Monday to the U.N. Human Rights Council, urged major powers to criminally pursue Pyongyang’s leadership before its “ever-worsening” rights record, including mass executions and labour camps, threatened world peace.