Zhang Liangui, North Korea expert at the communist party's Central Party School, tells Global Times that Pyongyang will never give up its "bargaining chip" of developing nuclear weapons and that it values relations more with Washington than Beijing.

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Mike Chinoy, a former CNN correspondent who has visited North Korea 15 times, said the current confusion about Pyongyang's capabilities recall a similar episode in 1998, when U.S. spy satellites discovered an underground complex at Kumchangri, not far from North Korea's main nuclear facility at Yongbyon.

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Fireworks lit up the skyline in the North Korean capital, Pyongyang, while South Korea ushered in the new year with the traditional ringing 33 times of the 15th Century Bosingak Bell in the capital, Seoul.

BBC: New year revellers welcome 2013 with fireworks