The United States is concerned that the temporary shutdown of a North Korean nuclear reactor signals a move to double the North's nuclear arsenal.

An American expert who recently visited the North said the unloading of fuel rods in the reactor will provide some eight thousand spent rods for reprocessing into enough plutonium to produce six to eight nuclear bombs.

The New York Times said the reactor's suspension is aimed at securing plutonium, a key element of nuclear weapons production.

The Central Intelligence Agency reported to the U-S Congress that over the past two years, the North has reprocessed a large amount of spent fuel rods into weapons-grade material sufficient to produce at least six nuclear weapons.

The Institute for Science and International Security in Washington DC warned that if the North learns the complex procedures of nuclear reprocessing, it may secure enough plutonium to produce at least two nuclear weapons.

Based on U-S report, Seoul also confirmed Monday that the North has stopped operations at its Yongbyon reactor.

Pyongyang said earlier that the three-month suspension will start in April as part of its regular replacement of spent fuel rods.