''It's a very unfortunate development, but it's not a crisis'' special representative Stephen Bosworth said during a meeting with South Korean Foreign Minister Kim Sung Hwan, the Yonhap News Agency reported.

''It's not a crisis. We need more intelligence and analysis on what is the reality of the program there,'' Kim was quoted by Yonhap as responding.

The comments came after U.S. scientist Siegfried Hecker said in Saturday's New York Times that he had been shown hundreds of centrifuges already installed and operating at a new uranium enrichment plant during a recent visit to North Korea.

North Korea is already under a number of UN sanctions over its first nuclear test carried out in 2006. It pulled out of talks with Russia, Japan, China, the United States and South Korea over its nuclear program last April after the United Nations condemned the communist state's missile tests.