North Korea has begun disabling its primary nuclear facilities under the US supervision, officials here said.

While US State Department spokesman Tom Casey said on Monday that he was unable to give details about what work had been done at the nuclear complex in Yongbyon, 100 km north of Pyongyang, he said it had gotten under way.

“They are on-scene, and the work is under way,” he said of a US team of nuclear experts who arrived on Thursday in North Korea and travelled to Yongbyon at the weekend.

The disablement of the facility would be the fulfilment of the second phase of a February agreement in which Pyongyang agreed to dismantle its nuclear programme in exchange for economic and energy aid and the normalisation of diplomatic relations with Washington and Tokyo.

In the second phase, North Korea would disable the complex to the extent that bringing it up to operational capabilities again would take an extended amount of time and be expensive.

The first phase was completed in July when North Korea shut down the Yongbyon reactor. A month ago, North Korea said it would disable the facility and declare its nuclear stockpile by the end of the year.

Casey said the US team would remain at Yongbyon until the disablement of the complex’s five-megawatt reactor, its nuclear fuel-reprocessing plant and a fuel fabrication facility was completed.