ACTIVITY has been observed at a North Korean nuclear site that is consistent with an effort to restart a reactor, International Atomic Energy Agency chief Yukiya Amano has warned.

North Korea announced in April it would revive its reactor at the complex - which experts say is capable of producing plutonium for bombs - but said it was seeking a deterrent capacity.

Mr Amano said the Vienna-based IAEA continued to monitor developments at Yongbyon and added: "Activities have been observed at the site that are consistent with an effort to restart the reactor. However, as the agency has no access to the site, it is not possible for us to conclusively determine whether the reactor has been re-started."

Reclusive North Korea has defied warnings not to build atomic bombs and long-range missiles.