Short of war, how do you punish a state that has nothing? That is the dilemma facing South Korea and its allies in dealing with North Korea in the aftermath of the alleged attack on the Cheonan, a South Korean warship, with the loss of 46 lives.

Lee Myung-bak, South Korea's president, is taking a hard rhetorical line, saying that, unlike in the past when North Korean attacks went unpunished, this time Pyongyang must be held accountable.

In his first international speech since the official report on the March incident, Mr Lee told a weekend gathering of defence officials at the IISS Asia Security Summit in Singapore: “If we once again tolerate North Korea's blatant act of violence, then I believe that will not promote, but endanger, the peace and stability of the Korean peninsula.”