SEOUL, March 28 (Reuters) - North Korean leader Kim Jong Un called for scaling up the production of weapons-grade nuclear material to grow the country's arsenal, saying it should be ready to use the weapons at any time, state media KCNA said on Tuesday.

Kim made the remarks as he inspected the country's nuclear weapons programme, including new tactical nuclear weapons and technology for mounting warheads on ballistic missiles, and examined nuclear counterattack operation plans, KCNA said.

He was also briefed on an IT-based integrated nuclear weapon management system called Haekbangashoe, which means "nuclear trigger," whose accuracy, reliability and security were verified during recent drills simulating a nuclear counterattack, it added.

Kim ordered the production of weapons-grade materials in a "far-sighted way" to boost its nuclear arsenal "exponentially" and produce powerful weapons, KCNA said.

He said the enemy of the country's nuclear forces is not a specific state or group but "war and nuclear disaster themselves," and the policy of expanding North Korea's arsenal is solely aimed at defending the country, and regional peace and stability.

North Korea has been ramping up military tests, firing short-range ballistic missiles on Monday and conducting a nuclear counterattack simulation last week against the United States and South, Korea which it accused of rehearsing an invasion with their military exercises.

North Korea's military simulated a nuclear airburst with two tactical ballistic missiles during Monday's training, KCNA said in a separate dispatch.

A defence think tank also tested underwater strategic weapons systems on March 25-27, KCNA said.