Marking a significant step towards resolving a four-and-a-half-year stand-off with the US, North Korea has shut down its only operating nuclear reactor, the country's state-run media announced yesterday.

The 5MW facility at Yongbyon, about 60 miles north of Pyongyang, was closed on Saturday as international nuclear inspectors returned to the site for the first time since being asked to leave in 2002.

With Yongbyon offline, the site will no longer be able to process weapons-grade plutonium, though the plant is thought to have produced enough material already for six to eight warheads, including the one exploded underground in North Korea's first nuclear bomb test in October.