Top US intelligence official James Clapper asked South Korean officials during a recent visit for Seoul's bottom line in any future negotiation between the US and North Korea on a permanent peace treaty, a report said Saturday.

The 1950-53 Korean War ended with an armistice that has never been formalised by a peace treaty, meaning that the two Koreas technically remain at war.

Pyongyang wants a treaty to be the focus of any dialogue with Washington, while the United States, backed by Seoul, insists the first priority is the issue of North Korea's nuclear disarmament.

During a low key, two-day visit to the South last week, Clapper discussed possible responses to any fresh dialogue push by North Korea following its ongoing ruling party congress, South Korea's JoongAng Daily reported.

"There was an inquiry into how much South Korea is willing to concede in case the United States begins discussions with North Korea on a possible peace treaty," the newspaper quoted an unidentified senior foreign affairs and security official as saying.

US and North Korean officials have held a number of informal discussions in neutral venues in recent years, but they are understood to have stalled over the basis for any official dialogue.

"The reason that Clapper referred to peace treaty talks is to cope with the North making a fresh proposal for a peace treaty following the congress," another official told the newspaper.

Any peace treaty would have to be agreed between the two sides involved in the Korean conflict -- North Korea and China on one hand and the US-led United Nations on the other.

Seoul and Washington insist North Korea must take tangible steps towards denuclearisation before a peace treaty can be put on the table.

"There is no change to this stance," a South Korean foreign ministry official said when asked to comment on the news report.

During his visit, Clapper reportedly held closed-door talks with South defence, military and presidential officials.

Nobel laureates call for easing N Korea sanctions
Beijing (AFP) May 7, 2016 - Sanctions that have pinched North Korea's health care system should be eased, a group of Nobel laureates said Saturday, after a rare visit to the nuclear armed state that coincided with its ruling party congress.

Embargoes on the flow of goods into the isolated country have squeezed the quality of medical care and research, they said, following visits to hospitals and labs in Pyongyang.

"You cannot turn penicillin into a nuclear bomb," Aaron Ciechanover, who won the top prize for chemistry, told a media conference in Beijing a day after returning from the visit.

"You don't pressurise via making people sicker," he said: "That's not the right way to go."

The three prize winners from Norway, Britain and Israel spent a week in the country on a humanitarian trip organisers said would be an exercise in "silent diplomacy".

Their visit came as North Korean leader Kim Jong-un opened the country's first ruling party congress since 1980 by hailing its "magnificent... and thrilling" nuclear weapons programme.

World powers have tightened sanctions on the isolated state this year after Pyongyang carried out several ballistic missile launches and its fourth nuclear bomb test -- and analysts predict another could be in the works.

While the sanctions do not target medical aide, tough South Korean restrictions have stopped some medicines from reaching its northern neighbour, according to a recent report in the Washington Post.

"Many of the things the doctors would like, the professors would like, they just can't have them because of the embargo," said Richard Roberts, who won the prize for medicine.

The trio of Nobel prize winners, which also includes economics laureate Finn Kydland, visited a children's hospital, science facilities and a farm, among other sights.

The laureates described clean, modern facilities -- a stark contrast to other accounts of the country as brutally impoverished -- and two said they had invited young researchers to work in their labs.

The few opportunities for foreigners to visit the country are tightly stage-managed, with the government carefully controlling most interactions with the North Korean people.

Planning for the trip began more than two years ago after the Vienna-based International Peace Foundation (IPF) received an unsolicited email from the Korean National Peace Committee.

South Korea's government asked the group to postpone the trip when it emerged that it would coincide with the congress, citing fears it could be "misused", IPF chairman Uwe Morawetz said, but scheduling restrictions made it impossible.