"We are not going to have a nuclear deal without resolution of that issue," he said of the uranium enrichment.
In the coming weeks, the six countries were likely to form groups of experts to negotiate the "technical underbrush" of a potential disarmament agreement, Hill said.
"We realized how much work we have ahead of us," he said
A Chinese statement said the parties had agreed to hold a second session of the fifth round at the earliest possible date.
"The parties reaffirmed that they would fully implement the (September) joint statement in line with the principle -- commitment for commitment, action for action," the statement said.
Hill said it might be difficult to reconvene in December, because of other commitments.
The fifth round of talks made clear the continuing friction between Washington and Pyongyang. North Korea also raised objections to a U.S. ban on a Macao-based bank accused of laundering counterfeit U.S. money made in Pyongyang, Hill said. Kim said that his country and the U.S. would hold one-on-one meetings to discuss financial sanctions.
A source close to the talks quoted North Korean delegates as saying on Thursday that they had no "will" to negotiate with the United States, Japan's Kyodo news agency said. Pyongyang has voiced anger over Washington's move to freeze assets of North Korean companies it suspects of dealing in weapons of mass destruction.