Seoul - North Korea has several thousand tons of chemical weapons, a report from a think tank published on Thursday said.

"Pyongyang's nuclear capabilities are the greatest threat, but it also possesses a large stockpile of chemical weapons and is suspected of maintaining a biological weapons programme," the report published by the International Crisis Group (ICG) said.

The North Korean People's Army (KPA) is widely thought to have 2,500 to 5,000 tons of chemical weapons, including sarin, mustard gas and phosgene, which it could use in a war.

The ICG confirmed estimates the South Korean Defence Ministry made in recent years about the amount of chemical and biological weapons North Korea possesses.

South Korea has said that its northern neighbour also has the ability to cultivate viruses.

"The KPA might employ it [the chemical weapons stockpile] as part of its strategy to achieve a quick victory against the South before the US could intervene effectively," the report said.

"The stockpile does not appear to be increasing but is already sufficient to inflict massive civilian casualties on South Korea."

North Korea could deliver the weapons to their targets using long-range artillery or ballistic missiles, the report added.

The report was published amid rising tensions on the Korean Peninsula. North Korea has threatened war and said it would build more nuclear weapons in response to a United Nations Security Council resolution authorizing toughened sanctions against the Stalinist state following its May 25 nuclear test. (dpa)