South Korea is the North's usual rhetorical target, but the US has also been singled out for special treatment. ''We are not disguising the fact that the various satellites and long-range rockets that we will fire and the high-level nuclear test we will carry out are targeted at the United States,'' North Korea's National Defence Commission said last month, the state news agency KCNA reported. The possibility of a North Korean nuclear warhead reaching as far as Los Angeles or Darwin is no longer considered fanciful after the North successfully tested a ballistic missile in December. The North may also be close to developing a ''miniaturised'' warhead that can be fixed to it, analysts and diplomatic sources say. A third North Korean nuclear test may place its only ally, China, in a tighter bind, as the country would then be surrounded on all sides by nuclear weapons states.

Sources close to the family of the new leader, Xi Jinping, say he is moving to firmly grasp control of military and foreign affairs, and changes in direction are not inconceivable. But Chinese regional security analysts seem convinced that Beijing could not force Pyongyang to give up its nuclear weapons program even if it tried. ''There are hardly any circumstances that could divert North Korea from its path to becoming a nuclear power,'' said Cai Jian, professor of Korean studies at Shanghai's prestigious Fudan University. Professor Cai said the timing of North Korea's nuclear test was uncertain, and would be designed to extract maximum geopolitical leverage, but it would happen because it was necessary for refining the weapons technology. And he said China's strategic impetus to shelter North Korea has sharpened since the Obama administration's ''pivot'' towards Asia.

''As China grows, the United States adjusts its strategy towards east Asia to deter and encircle China,'' he said. ''What China needs is the survival and existence of the North Korean regime to help China maintain the balance of power in the region,'' he said. An article in Wednesday's Global Times, a nationalistic Communist Party tabloid, said China should not be held hostage to North Korean bad behaviour. ''Even if the whole Korean peninsula becomes more pro-American, it will not block the rise of China,'' said the editorial. in the paper's Chinese edition Professor Cai said the editorial might signal China would raise the volume of its protests after a North Korean nuclear test but it would not affect the basic strategic equation.

Washington is aware that it lacks bargaining leverage with North Korea or China so long as military options are off the table, some analysts and diplomats said. Talk of a pre-emptive South Korean, US-backed strike is intended to put pressure on China to use any leverage it has to restrain the North, they said. ''If there is a clear intent that North Korea is about to use a nuclear weapon, we will eliminate it first even at the risk of a war,'' said South Korea's General Jung on Wednesday, the Korea Times reported. ''A pre-emptive attack against the North trying to use nuclear weapons does not require consultation with the United States and it is the right of self-defence,'' he said. Nevertheless, a close discussion including a pre-emptive strike option between South Korea and the US meant sharing comprehensive strategies aimed at containing North Korea, he said.

with Sanghee Liu