The leader of South Korea\'s main opposition Democratic Party (DP) on Monday embarked on a four-day trip to China to discuss regional security, including North Korea, and ways to promote bilateral economic ties. Rep. Sohn Hak-kyu is to meet with Chinese Vice President Xi Jinping, who is earmarked to become China\'s next president, and senior politicians in Beijing to share views on regional diplomatic issues, party officials said. China is North Korea\'s last remaining major ally and has propped up its impoverished, provocative neighbor with food and energy assistance and diplomatic support. Beijing is also the host of six-party talks on Pyongyang\'s nuclear programs. The visit by the opposition leader, considered a 2012 presidential hopeful, comes after his earlier visit to Tokyo in June to meet Japanese political leaders. During a meeting with Japanese Prime Minister Naoto Kan, Sohn said South Korea should sternly act against North Korea\'s human right abuses and nuclear weapons development, stressing \"engagement policy based on principle.\" His remarks, however, came under attack by other party members, including Chung Dong-young, a former unification minister, who accused him of echoing the conservative ruling party\'s hard-line policy toward the North. The DP has championed the so-called \"sunshine policy\" aimed at facilitating broad social and economic exchanges as a way to lead the reclusive country to the outer world stage.