US negotiator Christopher Hill returned to South Korea on Friday after a high-stakes mission to North Korea aimed at saving a shaky nuclear disarmament apact.
The chief nuclear envoy crossed the heavily fortified border at 3:30 pm (0630 GMT), a US embassy spokesman said.
On arrival later in Seoul, Hill was expected to brief his South Korean and Japanese counterparts, Kim Sook and Akitaka Saiki, about the outcome of his two-day visit to the hardline communist state.
Hill had extended his stay in Pyongyang by one day. But there was no immediate word on whether he had persuaded the North's regime to cancel its plans to resume production of weapons-grade plutonium.
The State Department said on Thursday the assistant secretary of state had contacted Washington from Pyongyang.
"He didn't provide anything that I would consider a full report," said spokesman Sean McCormack.
"I think that's understandable given the communications issues."
McCormack said Hill would travel on from Seoul to Beijing for talks with China, host of the six-party forum which has been trying for five years to negotiate an end to the North's nuclear programme.
US officials say Hill was expected to offer the North a face-saving compromise in hopes of settling a dispute over nuclear inspections which has put the February 2007 disarmament agreement in jeopardy.
Pyongyang accepted the aid-for-disarmament deal just four months after staging its first nuclear test.
It shut down its Yongbyon nuclear complex in July last year and began disabling it in November. And in June it handed over a declaration of nuclear activities to China.
But now the North is angry that the US failed to respond by removing it from a terrorism blacklist, as required under the accord. It says it will soon begin work to restart a plutonium reprocessing plant, which could produce more bomb-making material from spent fuel rods.
Before delisting occurs, the US demands that the North agree on inspection procedures to ensure it is telling the truth in its declaration.
The North says verification is not part of this stage of the agreement, and accuses Washington of violating its dignity by seeking Iraq-style "house searches" for atomic material.
US officials say a compromise could see the North submitting written acceptance of a verification plan to its ally China rather than to all the negotiators at once.
South Korea, Japan, Russia and the US are also part of the forum along with North Korea itself.
The Washington Post last week reported that under the proposal, the US would provisionally remove the North from the blacklist and China would then announce the North's acceptance of the plan.
This would allow the North to claim that the US acted first.
The question is whether the secretive North can swallow the US-inspired verification plan, which reportedly calls for access to undeclared suspected nuclear facilities and for inspectors to take samples of material.
The State Department says Hill will not offer changes to the "substance" of an inspection plan.