North Korea apparently has shut down its main nuclear reactor, in a possible prelude to reprocessing spent fuel rods into weapons material.

North Korea's spent nuclear fuel rods that are kept in a cooling pond are seen at the nuclear facilities in Yongbyon in 1996

A South Korean Foreign Ministry official told local media that his government and the United States have verified that North Korea's Yongbyon nuclear power plant has been shut down.

Security experts say the plant may have been shut down to permit North Korea to remove spent plutonium and reprocess into weapons fuel.

Mark Gwozdecky, of the International Atomic Energy Agency, says the plant may contain as many as eight thousand spent fuel rods. Experts say that could yield as many as six to eight nuclear weapons. Mr. Gwozdecky says the agency is unsure how quickly Pyongyang could turn the rods into weapons material.

"We don't know the state of readiness of their reprocessing facility … if it's fully operational, then they have a reprocessing capability that can separate the spent plutonium in a matter of months."

Since February, the North Koreans have repeatedly said they have nuclear weapons and intend to make more - despite having signed several agreements in the past to remain nuclear free. Pyongyang has suspended participation in six-nation talks aimed at ending its nuclear programs.

Shin Maeng-ho, a director of South Korea's presidential task force on the North Korean nuclear issue, says they are watching the situation carefully, but they are not drawing any hasty conclusions.

"It is difficult for me to say about the North Korean intention, whether they have the intention to reprocess it or not," he said.

Despite repeated assurances by that Washington does not plan to attack or invade North Korea, Pyongyang says it needs nuclear arms to deter what it says is a hostile attitude by the United States.

U.S. officials say they are still optimistic a peaceful, diplomatic solution can still be reached in the framework of six party talks, which also involve South Korea, China, Japan, and Russia.