U.S. State Department spokeswoman Victoria Nuland said the meetings were constructive.
"There was some narrowing of differences, but important issues do remain," she said. "We now think that we've both got to go back to our capitals, we've got to evaluate what we've heard. And we have agreed that we will be in touch at an appropriate moment, and if there is more to say through the New York (U.N. diplomatic missions') channel, or if there are other channels that we have."
The six-party talks among the two Koreas, the United States, Russia, China and Japan on the North's denuclearization have remained stalled since 2009 when the North walked out. Since then China has been pressing the North to return to the talks.
U.S. officials, while being cautiously optimistic about the Geneva talks, said it could be months before it is known if North Korea would take the "concrete" steps needed to resume the talks, the Voice of America reported.
Stephen Bosworth, the U.S. special envoy for North Korea, said the talks in Geneva were positive and generally constructive.
Vice Foreign Minister Kim Kye Gawn, representing North Korea, said there were "big improvements" in some areas and that other differences would be resolved when they meet again. The two sides held their first round of talks in New York in July.
U.S. demands for the resumption of talks include North Korea stopping its uranium enrichment program.
China is urging North Korea to improve relations with the United States and South Korea. Chinese Vice Premier Li Kequiang has been visiting North Korea in the backdrop of the Geneva talks.
North Korea leader Kim Jong Il, who met with Li, called for the talks to resume soon.