South Korea and Japan have failed to enlist Chinese support for their tough stance against North Korea.
At a summit on the South Korean island of Jeju, Chinese Prime Minister Wen Jiabao again refused to blame - or even name - North Korea over the sinking of the South Korean warship Cheonan in March, which killed 46 sailors.
Instead, he spoke of dispelling the incident's impact.
All three leaders agreed that the sinking is a serious challenge to peace and stability in the region.
Japanese Prime Minister Yukio Hatoyama said he fully accepted the evidence that the ship was hit by a torpedo fired from a North Korean submarine.
But Mr Wen went no further than expressing his condolences for the families of the victims and speaking of the need to resolve the tension.
Meanwhile, North Korea, which accuses the South of fabricating the attack, has held a mass rally in the capital, Pyongyang.
Tens of thousands of people denounced the South Korean authorities as mad, war-mongering puppets.