South Korea''s chief nuclear envoy Lim Sung-nam left for Russia Wednesday to coordinate their joint strategy on how to revive the stalled six-party talks on ending North Korea''s nuclear weapons programs. The three-day visit by Lim Sung-nam to Moscow came a day after North Korea and the United States concluded two days of "very positive" talks in Geneva, but no agreement to restart the six-nation negotiations, involving the two Koreas, the US, China, Russia and Japan, was reached, South Korea''s News Agency (Yonhap) reported.