Former U.S. envoy on N. Korea meets N. Korean official in Berlin

U.S. and North Korean officials have held informal talks over Pyongyang's nuclear program in Berlin, a diplomatic source said.

Among participants in the meeting were Stephen Bosworth, a former top U.S. envoy on North Korea, and Ri Yong Ho, North Korea's chief negotiator for six-way talks on the denuclearization of the Korean Peninsula, according to the source.

They appear to have exchanged notes on the possible resumption of the six-party talks and could have also discussed economic problems of the North, according to the source.

The meeting follows a report by South Korea's Yonghap News Agency on Wednesday that a meeting will be held in Berlin where Bosworth and Ri will take part, citing a source in Washington. Bosworth was the top U.S. envoy on North Korea during President Barack Obama's first administration.

North Korea has been calling for restarting the stalled negotiations, which also involve China, Japan, Russia and South Korea, without any preconditions. The United States upholds the position that the North must take concrete actions toward denuclearization.