Multi-nation talks on North Korea's nuclear disarmament continue for a second day in Beijing, with the United States telling North Korea it needs to shut down a nuclear reactor if it wants to build the trust needed to end the dispute with the international community.

U.S. chief negotiator Christopher Hill went into the second day of talks here in Beijing Thursday saying North Korea must shut down the reactor at its main Yongbyon nuclear facility now, as it agreed to do at the last round of talks in September.

"You know how you build up trust? You live up to the agreement," said Mr. Hill. "You come up with solid implementing schemes that enable you to move forward and show that what you've agreed to do in the agreement, you're actually doing and that's the best way to build up trust."

This is the fifth round of disarmament talks in two years among China, Japan, the two Koreas, Russia, and the United States. They are discussing how to implement a joint set of principles in which North Korea agreed to give up its nuclear programs in exchange for aid and security guarantees.

Mr. Hill suggested that keeping the reactor in operation is an obstacle to resolving the nuclear crisis.

"Yongbyon has continued to operate, and in operating it's continuing to produce material that can, through reprocessing, be turned into weapons grade plutonium. And so every day that goes on the amount of this plutonium theoretically can increase and so that's our concern," he added. "That means we have a bigger problem than when we ended on September 19."

The crisis flared in 2002 when the United States said North Korea had acknowledged it was developing a uranium-based nuclear weapons program in violation of international agreements. North Korea, which has since expelled international weapons inspectors, says now it possesses nuclear weapons - a claim experts say may be true.

Diplomats expect this round of negotiations to continue through Friday.