The IAEA has said it is firmly opposed to North Korea operating its nuclear facilities without the presence of UN safeguards inspectors.
The UN nuclear watchdog was responding to a US claim that North Korea restarted the main reactor at its controversial nuclear plant at Yongbyon within the past 24 hours. A US official, speaking to the Reuters news agency on condition of anonymity, said the intelligence was obtained through satellite photographs.
The IAEA has told Reuters that if this is true, the agency deplores the operation of the DPRK (North Korean) nuclear facilities without the presence of safeguards inspectors.
The US has said it believes that the Communist state has not yet started reprocessing nuclear fuel, which could be used to produce material for nuclear weapons.
The authorities in South Korea have restated their belief that the North's nuclear programme is a serious threat to world peace.
Analysts in Seoul have said the move is a test for their new President Roh Moo-hyun.