HARBIN, China (Reuters) - Russian President Boris Yeltsin on Tuesday visited Harbin, a Chinese city with strong Russian links, and appeared upbeat on prospects for stronger economic cooperation with China. Moscow views deeper economic ties as crucial for cementing its new political friendship with Beijing. On Monday, during his official visit to Beijing, Yeltsin and Chinese President Jiang Zemin signed a declaration that ended disputes over border demarcation and outlined key areas in which the countries would develop economic ties. A separate inter-governmental memorandum aimed at kick-starting stalled economic ties was also signed on Monday. Russia and China, once close communist allies in the 1950s, later battled for supremacy in the communist world. This rivalry climaxed in a series of bloody border clashes in 1969. The two countries started rapidly improving political relations in the late 1980s and now say they have developed a "strategic partnership". But good political relations have not so far been matched by strong economic ties. Lack of control and government support, acknowledged by both sides, has led to a steady decline in cross-border trade over the past two years. Yeltsin, accompanied by the governors of four Russian regions, held talks with Chinese officials to try to sort out existing problems. The highlight of the fifth Sino-Russian summit was a declaration laying to rest the wrangles over the implementation of a 1991 accord that mapped out the entire 4,300-km (2,800-mile) frontier.