SEOUL - North Korea has several thousand tons of chemical weapons it can mount on missiles that could be used on a rapid strike against the South, said a report released on Thursday by the International Crisis Group (ICG).

North Korea in recent weeks has raised tensions in North Asia, responsible for one-sixth of the global economy, with missile launches, threats to attack the South and a May 25 nuclear test that led to U.N. sanctions.

The report from the prestigious non-governmental organisation said the consensus view is the North's army possess about 2,500-5,000 tons of chemical weapons that include mustard gas, sarin and other deadly nerve agents.

If there is an escalation of conflict and if military hostilities break out, there is a risk that they could be used. In conventional terms, North Korea is weak and they feel they might have to resort to using those, said Daniel Pinkston, the ICG's representative on Seoul.

The North has been working on chemical weapons for decades and can deliver them through long-range artillery trained on the Seoul area -- home to about half of South Korea's 49 million people -- and via missiles that could hit all of the country.

The stockpile does not appear to be increasing but is already sufficient to inflict massive civilian casualties on South Korea, the ICG report said.

The report said North Korea has also worked on a biological weapons program but Pinkston does not think Pyongyang has fully developed that weapons program.

In a separate report released simultaneously, the ICG said North Korea has deployed more than 600 Scud-type missiles that can hit all of South Korea and as many as 320 Rodong missiles that can strike Japan.

The ICG said earlier this year intelligence it acquired indicates the North has developed a nuclear warhead it could mount on an Rodong missile, and this latest report repeats the claim.

Many weapons experts believe the North is years away from being able to miniaturize a nuclear weapon to mount on a warhead and requires several more nuclear tests to develop one.

The ICG said the North's nuclear threat is the region's most urgent security issue but if progress is made on rolling back Pyongyang's atomic ambitions, there could be a way to find a solution to the threats posed by chemical and biological weapons.

MISSILE TESTS

North Korea has warned ships to stay away from waters off its eastern city of Wonsan until the end of the month, according to a Japan Coast Guard spokesman, which could indicate a possible missile test.

The North fired a barrage of short-range missiles off its east coast just after its nuclear test in May.

Separately, North Korea may be looking to test fire a long-range missile over Japan in the next few weeks, Japan's Yomiuri newspaper cited a defence ministry analysis as saying.

North Korea threatened to fire an intercontinental ballistic missile if the U.N. Security Council did not apologise for punishing Pyongyang for an April rocket launch, widely seen as a disguised missile test that violated U.N. resolutions.

The rocket launched in April flew about 3,000 km (1,860 miles), well short of the 4,800 km needed to reach the Alaskan coast. The rocket, called the Taepodong-2, is designed to fly as far as U.S. territory.

Analysts say the North's defiant moves are aimed at building internal support for leader Kim Jong-il, who appears to be laying the foundation for his youngest son to take over the impoverished state. The 67-year-old leader of Asia's only communist dynasty is believed to have suffered a stroke last year.

North Korea responded to fresh U.N. sanctions to punish it for its nuclear test by saying at the weekend it would start a uranium enrichment program, which experts said could give it a second route to an atomic bomb, and weaponize all its plutonium, believed to be enough for at least six bombs.

(Additional reporting by Chisa Fujioka and Yoko Kubota in TOKYO; Editing by Jerry Norton)

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