Seoul, South Korea ? North Korea has begun moving fresh fuel rods into a reactor, a key step in reactivating nuclear facilities that could eventually produce weapons, a South Korean news agency said today.

It appeared to reflect the Communist north’s determination to restart the dormant plant, the center of a diplomatic standoff with the United States.

The Yonhap news agency, quoting an unidentified South Korean government official, said the communist North began moving fuel rods into the five-megawatt reactor at its main nuclear center in Yongbyon, 50 miles north of its capital, Pyongyang.

The report followed an announcement Wednesday by officials in South Korea that the North has let the U.N. International Atomic Energy Agency send more inspectors to its nuclear facilities, even as communist engineers move freely around a reactor in violation of arms control agreements.

The agency has three inspectors staying in North Korea checking the activities of North Koreans. The number of inspectors was increased from two to three this week.

In a confrontation with the United States, North Korea on Dec. 12 decided to restart its frozen nuclear facilities and then removed U.N. monitoring seals and cameras from the reactor and three other key nuclear facilities.

“We’ve confirmed through IAEA that North Korea began moving fuel rods into the reactor on Wednesday,” Yonhap quoted its source as saying.

The Yonhap report said that there were no signs that the North Koreans were using spent fuel rods, a step that could mark a move toward building a bomb. U.S. officials say that the North’s 8,000 spent rods hold enough weapons-grade plutonium to make several nuclear bombs. North Korea is suspected of already having at least one atomic bomb.

South Korean President Kim Dae-jung said today that his government will never tolerate the North’s efforts to develop nuclear weapons but stressed that the issue should be resolved peacefully through dialogue.

“We must closely cooperate with the United States, Japan and other friendly countries to prevent the situation from further deteriorating into a crisis,” Kim told a special Cabinet meeting.