United States and North Korean officials have completed a third day of talks in New York amid growing fears for the agreement, under which North Korea promised to freeze its nuclear programme.

American officials are demanding access to a vast underground site which they suspect might be part of a new nuclear complex.

The former American official who negotiated the original agreement in 1994, Robert Gallucci, told the BBC that the deal was in trouble unless North Korea changed its position.

Meanwhile, Japanese public television, NHK, reported that American spy satellites had detected three new underground sites in North Korea.

It said they appeared to be launching bases for ballistic missiles.

The special American envoy, William Perry, is continuing a visit to the region to reassess American policy towards North Korea.