The U.S. special envoy on North Korea's human rights says there is neither an appropriate nor inappropriate time for Washington to raise the issue.

Jay Lefkowitz told a news conference at the U.S. Embassy in Seoul Friday that he wants progress in the six-party nuclear talks, but that the world should know the state of human rights in the North.

He said the North cannot be trusted unless it guarantees freedom for its people, urging more efforts to improve the lives of North Koreans.