The top U.S. nuclear envoy said Saturday that his country aims to shut down, not freeze, North Korea's only operational nuclear reactor.

U.S. Assistant Secretary of State Christopher Hill said Washington and Pyongyang have an understanding that a nuclear deal in this week's session, if reached, should call for a complete "shutdown" of the North's key nuclear facilities, instead of a mere operational freeze.

Hill earlier had said that "fundamental" issues have been resolved but "one or two" sticking points still remain.

When asked early Saturday whether North Korea's nuclear facilities at its main nuclear complex in Yongbyon were one of the remaining issues, Hill said there was no dispute over the need to shut them down.