South Korea's main opposition leader Moon Jae-in urged the country Sunday to resume efforts to restart the stalled multilateral talks aimed at denuclearizing North Korea.

The six-party talks involving the two Koreas, China, Japan, Russia and the United States have been suspended since late 2008 due to Pyongyang's backtracking on its past agreement to abandon its nuclear weapons program in exchange for economic and political concessions.

In his speech marking the 70th anniversary of Korea's liberation from Japan, the head of the main opposition New Politics Alliance for Democracy cautioned South Korea against depending on the U.S. and China to bring about nuclear disarmament of North Korea.

"Nothing will be resolved if we continue to depend on China or wait until the U.S. takes action," he said at the National Assembly in southwestern Seoul. "We can't and shouldn't rely on others."

To quickly resume the six-party dialogue, Moon suggested a two-track diplomacy in which South Korea would try to improve inter-Korean ties, as well as North Korea-U.S. relations.

"We are the impetus for conversation because we want it most," he said, adding South Korea is the country most threatened by the North's nuclear program.

The 2012 presidential candidate also insisted that South Korea increase its growth potential by expanding business opportunities in the North.