Seoul, South Korea ? North Korea’s moves to restart a nuclear reactor that U.S. officials believe was used to make one or two atomic bombs amount to “nuclear brinkmanship” and are “very worrying,” the U.N. nuclear watchdog said Thursday.

North Korea, however, said it was “peace-loving” and had no plans to develop weapons at the site.

Across the fortified border from North Korea, South Korean President-elect Roh Moo-hyun warned the North today that reactivating the reactor could endanger the communist state’s own safety.

He added that North Korea’s defiant attitude could make it difficult for him to continue his predecessor’s policy of seeking reconciliation with Pyongyang after he takes office in February.

“Whatever North Korea’s rationale is in taking such actions, they are not beneficial to peace and stability on the Korean Peninsula and in Northeast Asia, nor are they helpful for its own safety,” Roh said in a statement.

On Thursday, South Korean President Kim Dae-jung said his nation would never tolerate its neighbor’s nuclear development. But he said the South sought a peaceful end to a dispute that resembles a 1994 crisis about the same reactor that some say nearly led to war.

Australia today shelved plans to open an embassy in North Korea amid the rising tensions linked to Pyongyang’s moves to reactivate its nuclear weapons program.

Foreign Affairs Minister Alexander Downer said Australia told North Korea that restoring full diplomatic links could not proceed while it violated nuclear nonproliferation obligations.

North Korean workers have moved 1,000 fresh fuel rods to a storage site near the Soviet-designed, 5-megawatt reactor at Yongbyon that was frozen in a deal with Washington that ended the 1994 crisis, the U.N. International Atomic Energy Agency said. A total of 8,000 such rods are needed to start the reactor.

“Moving towards restarting its nuclear facilities without appropriate safeguards, and towards producing plutonium raises serious nonproliferation concerns and is tantamount to nuclear brinkmanship,” Mohamed ElBaradei, director of the Vienna-based agency, said in a statement.