The top US envoy to negotiations on North Korea's nuclear programme has left Pyongyang after three days of talks.

Stephen Bosworth is the first official from the Obama administration to hold direct talks with the North Korean government.

He has made no formal comment so far on the outcome of the meetings, although he is expected to brief South Korean officials later on Thursday after landing in Seoul and then speak to reporters.

Before flying out of Pyongyang, China's Xinhua news agency quoted Bosworth as saying the talks had been "very useful".

In Washington officials at the US state department said they had no information on how the talks had gone or who Bosworth had held talks with.

Bosworth's visit had been aimed at persuading North Korea to return to six-nation disarmament talks and a deal which would see the North giving up its nuclear weapons in return for aid and security guarantees.

North Korea announced in April that it was walking away from the talks, calling the disarmament process "dead".

It followed the walk-out shortly afterwards by conducting a second nuclear weapon test and then a raft of missile tests.

North Korea's official media had made no comment on Bosworth's visit other than a one-line despatch on Thursday noting that he and his delegation had left.

Analysts have speculated that North Korea is pressing for a formal peace treaty with the US, ending the 1950-53 Korean War, as a precondition for rejoining the six-party disarmament talks.

'Hostile' attitude

North Korea walked away from the six-party talks process in April [AFP]

North Korea has said it sees the lack of a peace treaty with the US as evidence that the US has a "hostile" policy toward it.

Washington has said it will only hold direct talks as a precursor to a revival of the six-party process, and will not agree to any major steps without the agreement of other parties.

Briefing reporters in Washington earlier this week, a US official said Bosworth would not be offering any new inducements to North Korea to return to talks.

The official, speaking on condition of anonymity, said any return to the dialogue would enable North Korea to once again seek economic assistance offered under the 2005 disarmament deal.

"If they are ready to go, we are confident that the chair of the talks would be ready to reconvene those talks," the official said, referring to the stalled six-party negotiations.

"If there are specific issues that the North wants to raise in terms of how to get them restarted, obviously we would listen to that."