When Lee Myung-bak, South Korea's president, reacted to the March 26 sinking of a South Korean warship with the loss of 46 lives by calling for an independent inquiry, the initial reaction was that he was playing for time. He probably was. To rush to the conclusion that North Korea had torpedoed the ship would have put him under pressure to retaliate, risking a dangerous military escalation with his unpredictable, nuclear-armed Stalinist neighbour. Now an international inquiry has confirmed that Pyongyang was responsible, the world has the option to take more measured, co-ordinated action. But to mount a credible international response, China – Pyongyang's most important ally – needs to be on board. The ball is now in Beijing's court.

This makes life uncomfortable for China's leaders. On the one hand, they have little interest in piling pressure on North Korea. A possible outcome of squeezing Pyongyang till the pips squeak is to provoke a crisis or even a collapse of the regime. Beijing fears North Korean instability and the possibility, in extreme circumstances, of millions of refugees crossing the border into China. Every indication suggests it would prefer a volatile North Korea to a failed state. On the other hand, the status quo is untenable. North Korea looks like a grotesque parody of Mao's centrally controlled China, precisely the sort of system that Beijing has left behind. Many younger Chinese must find it embarrassing that Beijing is propping up such an odious regime.

Wen Jiabao, China's premier, has shown some signs that Beijing feels the pressure. In Seoul, he said China would not protect whoever sank the warship, offering a glimmer of hope that Beijing might not block action at the United Nations Security Council next month. Yet China is still obfuscating, questioning the independence of the international inquiry – conducted by South Korea, the US, the UK, Australia and Sweden – and reiterating its tired call for stability on the peninsula. What kind of stability is it if Pyongyang is able to kill citizens of neighbouring countries with virtual impunity? Imagine how Beijing would have reacted if it were 46 dead Chinese sailors.