Seoul: North Korea said it had reached a 'certain agreement' with the US in one-on-one talks held in Berlin, the Korean Central News Agency (KCNA) reported Friday.

North Korea's foreign ministry said the Jan 16-18 talks were held in a 'positive and sincere atmosphere' in an attempt to "settle knotty problems in resolving the nuclear issue'.

US chief negotiator Christopher Hill had called the meetings in Berlin 'useful.

The Berlin meeting marks the first time that US and North Korean envoys have met alone away from Beijing since the so far fruitless negotiations over Pyongyang's nuclear programme began in 2003.

An earlier meeting of the six countries involved in negotiations - North and South Korea, China, Japan, Russia, and the US had made little progress.

Tensions have worsened since North Korea's test of a nuclear weapon last year. The Japanese and US foreign ministers have warned that tougher sanctions against North Korea would be considered if the hard-line country conducted further tests.