According to North Korea's state-run news agency KCNA, the authoritarian regime will use its "nuclear deterrent" in response to joint US-South Korean war games scheduled to take place this weekend.
Tensions in the region have been rising since the sinking of the South Korean warship Cheonan in March. Pyongyang denies involvement, but an international investigation found that the sinking was caused by a North Korean torpedo.
Relations between Pyongyang and Seoul had been warming tentatively throughout the past decade, but in 2008 the election of the conservative Lee-Myung bak as president of the South led to a more hardline stance against the North. The BBC's correspondent in Seoul says that while this latest stand-off is unlikely to lead to war, it will cause concern, not least in China:
China has been urging the US and South Korea to tread very carefully. It does not want to see tensions to rise further, and there have been clear signals from Beijing that it does not think that this sort of war game being held off the coast of the Korean Peninsula at this moment is a good idea.
China's real worry is that North Korea is already very isolated, it is being squeezed diplomatically and economically; and if it is squeezed too hard, it might live up to some of these words.