Amid growing speculation that North Korea is preparing for another nuclear test, South Korea warned Tuesday that Pyongyang has "thousands of tons of chemical weapons" across the country. The South also called for its northern neighbor to be suspended from the United Nations.

"North Korea is reported to have not just grams but thousands of tons 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," South Korea’s Foreign Minister Yun Byung-se told the U.N.-sponsored Conference on Disarmament in Geneva.

Yun also called for invoking the Chemical Weapons Convention and taking "collective measures" to counter North Korea's growing threat.

"It could take the form of suspension of North Korea's rights and privileges as a U.N. member," he said. Calling Pyongyang a "serial rule-breaker," Yun added: "North Korea's fast-growing weapons of mass destruction and missile capabilities including chemical weapons has become gravest threat to international peace and security."

North Korea has been accused of violating global nuclear weapons treaties with its ballistic missile tests. The Kim Jong Un-led country also conducted an intermediate-range ballistic missile test earlier this month, sparking concern across the world powers.

Yun’s comments come after recent satellite images showed continued activity at Punggye-ri nuclear test site, triggering speculation that the isolated nation may be preparing for another nuclear test.

"In particular, the shifting of supplies and equipment, as well as additional changes in the texture and pattern of small sections of the tailings pile at the North Portal, indicate continuing work inside the test tunnels," 38 North said. "These activities suggest continued preparation and maintenance of this portal for use in a new nuclear test. Should the decision be made to do so, North Korea could probably move forward with a nuclear test in short order but it remains unclear when such a test might take place."