North Korea must fulfill its pledge to fully dismantle its nuclear program, the main US envoy to disarmament talks insisted, as reports said Pyongyang may be willing to shut down a key reactor. US Assistant Secretary of State Christopher Hill made the comments in Seoul, where he met South Korean officials to discuss negotiating strategies before the six-nation talks resume in Beijing on Thursday. North Korea agreed in September 2005 to give up its nuclear program in exchange for aid and security guarantees. "Frankly, we cannot accept anything less than 100 percent implementation of the September statement," said Hill before a meeting with his South Korean counterpart, Chun Yung-woo. "The ultimate task for us is to complete denuclearization."