However, no details were available on the progress of the closed-door talks between the two countries, the first between the hardline communist state and Washington in five months. Critical negotiations come just days after the New York Times reported that the US intelligence had detected a secret underground complex where they believe Pyongyang is working to revive frozen nuclear weapons operations.

Under a landmark 1994 accord, Pyongyang agreed to freeze its suspect nuclear programme in return for two light-water reactors.

It also wants the United States to promise 5,00,000 tonnes of heavy fuel annually pending their construction by a United States-led consortium.

In addition to the nuclear issue, North Korean demands that Washington lift decades-old sanctions, and plans for a resumption of talksto broker a permanent peace on the tension-bound Korean peninsula, were also likely to be on the agenda.

For North Korea, its Vice-Foreign Minister Kim Gye Gwan is heading the Pyongyang delegation, while for the United States Deputy Assistant Secretary for East Asian and Pacific Affairs Charles Kartman is leading the US team.