"I come away from this two-day set of meetings buoyed by a sense that we are going to be able to achieve our full objectives, that is complete denuclearisation," he told reporters in the South Korean capital.
However, he added that he was "also burdened by the realisation of the fact that we're going to have to spend a great deal of time, a great deal of effort, a lot of work in achieving these."
Earlier, speaking at Pyongyang airport before his departure, Hill said the talks with senior North Korean officials had focused on "all aspects of the six-party process. And all aspects means all aspects".
Avoiding specifics he said there had been agreement from both sides on the need to move forward.
However, he made no mention of reports from Vienna on Thursday that a proposed initial visit next week by inspectors from the United Nations' nuclear watchdog had been put on hold.
"How can a country possibly give up it own deterrence?"
Lebambi, Harare, Zimbabwe
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The visit by officials from the International Atomic Energy Agency (IAEA) was cast into doubt after a spokesman at the North Korean embassy in Vienna said the government still had yet to receive frozen funds transferred from a Macau bank.
"We have no objections for the agency to prepare the visit as planned, but we are not ready to give our official confirmation for the scheduled visit of the agency due to the only reason of unfinished remittance," embassy spokesman Hyon Yong-man told reporters.
The dispute over the funds – thought to amount to about $25m - has proved to be a major roadblock to implementing an agreement reached at six-nation talks in Beijing in February.
Under the deal, North Korea agreed to shut down its main reactor at Yongbyon in return for energy aid and other benefits.
On February 13, 2007, at six-nation talks in Beijing, North Korea agreed to:
Start shut down of main Yongbyon nuclear reactor facility within 60 days of deal
Allow UN nuclear inspectors entry for all monitoring and verification
Discuss list of all nuclear programmes and materials including plutonium extracted from fuel rods
Declare all nuclear programmes and disarmament of all existing nuclear facilities
Begin talks on normalising diplomatic ties with the US and Japan, and resume high-level talks with South Korea
In return US, Russia, China, Japan and South Korea promise initial shipment of 50,000 tonnes heavy fuel oil within initial phase
The five nations agreed to establish working groups for initial and full implementation of action plan
Additional aid up to the equivalent of 1m tonnes of heavy fuel oil to be delivered to North Korea upon compliance
The agreement had set a deadline of mid-April, but that was missed amid the row over the frozen funds.
Hill's surprise visit to the North, the most senior US official to visit in five years, has raised hopes that progress may finally be made in persuading the North to halt its nuclear programme.
Hill had said this week that after months of delays the disputed funds had finally been transferred from Macau to a North Korean account at a Russian bank.
However, the comments from the North Korean embassy in Vienna on Thursday appeared to dispute that.
During his visit to Pyongyang, Hill held talks with his North Korean counterpart in the six-party process, Kim Kye-gwan.
The meeting has raised speculation that the US has changed its policy towards the North Korean nuclear issue.
Until now the Bush administration had rejected North Korean calls for bilateral talks, insisting that all discussions must take place with North Korea's neighbours within the six-party framework.