South Korean President Lee Myung-bak left for Beijing Saturday for annual summit talks with Chinese and Japanese leaders expected to center on North Korea and economic and other cooperation between the Northeast Asian powers.

The tripartite summit, set for Sunday between Lee, Chinese Premier Wen Jiabao and Japanese Prime Minister Yoshihiko Noda, comes amid concern North Korea could conduct its third nuclear test at any time to further escalate tensions after its failed long-range rocket launch last month.

Last week, the five permanent U.N. Security Council members -- the United States, Britain, China, Russia and France -- issued a joint statement urging Pyongyang to "refrain from further actions that may cause grave security concerns in the region, including any nuclear tests."

Sunday's three-way summit will be the fifth since the annual dialogue was launched in 2008. North Korea has always been a top topic for the meetings, but results have not been impressive due in large part to China's reluctance to get tough on North Korea.

It is unclear how far China will go this time in urging Pyongyang to refrain from provocations. But the leaders' declaration to be adopted after the summit is expected to be similar in tone to that of last week's joint statement by the permanent Security Council members, including China.

China is the North's last-remaining major ally and provides the impoverished, isolated nation with crucial economic aid and diplomatic support. Experts say Beijing dreads any instability in North Korea as it could hurt its economic and political interests.

Other topics for the meeting focus on increasing economic and other cooperation.

The three countries plan to sign an investment guarantee treaty calling for preferential treatment for investment from the partner nations. Also planned are two cooperation agreements, one of them on agricultural cooperation and the other on preventing desertification of forests and protecting wildlife, the presidential office said.

The investment pact will be the first economic treaty between the three countries.

After the trilateral session, the leaders plan to attend a lunch meeting of business leaders.

Later Sunday, Lee plans to hold one-on-one summits each with Wen and Noda to discuss bilateral issues. The meeting with Wen is expected to include free trade negotiations that the two countries launched earlier this month.

A separate meeting with Chinese President Hu Jintao is planned for Monday.

South Korea, China and Japan account for one-fifth of the global gross domestic product (GDP), half of the world's total foreign exchange reserves, 17.5 percent of all global trade and 22 percent of the global population.

The three are key trade partners for each other, but their political relations have often frayed over their shared history, including Japan's aggression against the other nations in the early 20th century, as well as over territorial rows.

They have held an annual three-way summit since 1999 on the sidelines of regional summits organized by the Association of Southeast Asian Nations (ASEAN). Since 2008, the sides have also held another regular summit that rotates among the three countries, and Sunday's meeting will be the fifth.

Last year, the countries opened a cooperation office in Seoul to handle joint projects. (Yonhap News)