North Korea says it has thousands of centrifuges operating at a previously undetected uranium enrichment facility and added that the plant is for civil nuclear power. It is not clear whether the centrifuges could be used to produce material for weapons. A US scientist has seen the facility, but could not confirm it was working. The claim comes as tensions remain high, after the North Korea shelled a South Korean island a week ago. Pyongyang says the shelling, which killed two people, was in response to Seoul's joint military drill with America near Yeonpyeong island. It is the first time that the North Korea has given details about what it calls its peaceful nuclear programme. Earlier in November, US scientist Siegfried Hecker visited Yongbyon and said the equipment he was shown was stunning. The North Koreans assured him the centrifuges were working, producing low enriched uranium which would be used as fuel in an experimental light water nuclear reactor they were building.