SEOUL — North Korea is capable of producing up to 12,000 tons of chemical weapons, which could cause massive civilian casualties in South Korea, a state think-tank said Wednesday.

Along with the North's nuclear capabilities, its chemical weapons stockpile is South Korea's most urgent security issue, Kwon Yang-Joo of the Korea Institute for Defense Analyses said in a report.

"The international community must show its strong will in seeking disarmament of North Korea's chemical weapons along with its denuclearisation," he said.

The South's defence ministry estimates that North Korea has some 2,500-5,000 tonnes of nerve gas, blood agents, mustard gas and other chemical agents.

Kwon said the North could produce up to 12,000 tonnes of chemical weapons deliverable by artillery, missile or aircraft.

He said that 5,000 tonnes of chemical agents could contaminate about 2,500 square kilometres (950 square miles), four times the area of Seoul.

The North would be capable of producing 625,000-1.25 million chemical bombs if it used all of its chemical stockpile at once, he said.

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