Host President Lee Myung-Bak and Japanese Prime Minister Yukio Hatoyama teamed up at the two-day summit to nudge China's Premier Wen Jiabao to declare Pyongyang responsible for the March sinking of the South Korean corvette.
But Wen gave no sign China is ready to back United Nations Security Council action against its ally over the sinking, which cost 46 lives.
"The urgent task now is to defuse the impact of the Cheonan incident, change the tense situation and avoid clashes," Wen told a joint press conference.
"China will actively communicate with relevant parties and lead the situation to help promote peace and stability in the region, which fits our common and long-term interests best."
South Korea announced reprisals including a trade cut-off after international investigators reported on May 20 that a North Korean submarine fired a heavy torpedo to sink the Cheonan.
The North denies involvement and has responded to the reprisals with threats of war, fuelling regional tensions.
In its latest response, Pyongyang said it did not possess the type of small submarine allegedly used for the attack, according to its official news media.
"Some say there is political instability in the region due to the Cheonan incident," President Lee told the summit Sunday, according to his senior spokesman Lee Dong-Kwan.
"We are not afraid of war, but we do not want war either. We have no intention to go to war."
Wen, whose country is the North's economic lifeline, has been cautious since arriving in South Korea Friday.
At a meeting with Lee that day, he said Beijing would, before determining its position, review the results of the international investigation into the Cheonan's sinking but would not protect whoever was responsible.
Lee told the press conference on the southern resort island of Jeju that he expects "wise co-operation" from neighbouring countries in handling the disaster.
Hatoyama, whose government Friday announced new sanctions against the North, said the three leaders agreed "that this is a serious issue related to peace and stability in Northeast Asia".
South Korea, at least in public, appeared fairly satisfied with the outcome of the Jeju summit.
"The inclusion of those remarks on the Cheonan in the joint press announcement in itself has significance," Lee's senior spokesman said.
But Paik Haksoon, of the Sejong Institute think-tank, said Wen's comments "indicate that China is still questioning the authenticity and authority of the investigation."
"There would be no point in taking this issue to the UN Security Council without securing support from China in advance," Paik told AFP.
Numerous countries have condemned the North for the sinking, one of the worst military attacks on the South since the 1950-53 war.
The North says the South's government faked evidence to incite tensions and boost its support before local elections this week.
South Korea, the United States and Japan need the support of veto-wielding member China to sanction -- or, at least, to censure -- the North at the Security Council.
The South's reprisals include preparations to resume cross-border loudspeaker propaganda broadcasts. The North has threatened to shell the loudspeakers now being installed along the frontier if the broadcasts go ahead.
The North has cut all ties with the South, scrapped pacts aimed at averting accidental flare-ups along their disputed sea border and vowed to attack any intruding ships.
It has threatened to shut down a jointly run industrial park at Kaesong, the last reconciliation project still operating.
The South plans to send a letter to the chairman of the UN Security Council this week, an unidentified official told Yonhap news agency.
"If it's too late, we might lose momentum," the official said.
Japan's Hatoyama had promised to give Seoul his country's "full support" when the case is referred to the council, his spokesman told AFP.
Hatoyama had also stated clearly that the resumption of six-party nuclear talks is unthinkable until the North offers a clear apology for attacking the Cheonan, South Korean officials said.
Source: AFP Asian Edition