The North cites what it calls US hostility as the main reason for its year-long boycott of the six-nation talks aimed at halting its nuclear weapons programme.

"The US hostile policy against our republic has not changed at all," the number two leader Kim Yong-Nam was quoted by South Korean pool reports from Pyongyang as saying.

"(The United States) puts pressure on us in various sectors such as politics, economics and military. But we are unfazed and stepping up economic construction."

The nominal head of state was speaking to South Korean civic delegates visiting Pyongyang to commemorate the 2000 inter-Korean summit.

Kim's remarks followed a call from US assistant secretary of state Christopher Hill, chief US nuclear negotiator, for North Korea to return to talks which group the United States, the two Koreas, China, Russia and Japan.

Hill, visiting Seoul to discuss ways to bring Pyongyang back to the negotiating table, raised Washington's urgency about the talks.

"We are talking about a lot of different steps. But we still believe in the six-party process," he said.

"The situation is not going to get any better for them (North Koreans). While time is not on our side, it is definitely not on their side either. It is in everyone's interest that we get this process going."

But he said Washington had set "no artificial deadline" for Pyongyang's return to the dialogue. With patience waning, some US officials have privately suggested the defiant North should be punished for not returning to the table.

The US envoy on Wednesday urged the North to set a concrete date for its return to the talks.

At a June 6 meeting between US and North Korean officials in New York, Pyongyang informed Washington that it would return to negotiations but gave no date.

North Korea has demanded what it calls a US "hostile" policy be dropped before reviving the talks. US criticism of human rights abuses in the communist state has also sparked angry protest from Pyongyang.

Hill hit back: "I don't think anybody should expect us to be silent ... on human rights. These are issues of international concern, and frankly these are issues of universal concerns."

North Korea on February 10 declared it had nuclear weapons. US officials have expressed concern it could conduct a nuclear test to take the standoff to a new level of crisis.

Some US officials have insisted that the standoff be taken to the United Nations Security Council to impose sanctions on the impoverished North.