Wen Jiabao must be cursing the timing. China's mild-mannered premier flies into Seoul tomorrow for a summit with South Korea and Japan where he probably hoped to talk about booming trade ties. Instead, he will be put on the spot over North Korea.

Ever since the South Korean government announced the results of its investigation last week into the sinking of the Cheonan warship, putting the blame on a North Korean torpedo, Beijing has been playing for time.

After two days of talks with Hillary Clinton this week when North Korea was top of the agenda, Dai Bingguo, China's top foreign policy official, would say only that “relevant parties” should “calmly and properly handle the issue and avoid escalation of tension”. With an eye on the clock, Chinese officials say they need more information about the investigation.