U.S. special envoy Stephen Bosworth concluded his three-day visit to the Democratic People's Republic of Korea (DPRK) on Thursday morning, saying his talks with DPRK officials were "very useful."

"It was a very useful set of meetings," Bosworth told Xinhua at the Pyongyang Sunan Airport before leaving for South Korea.

He declined to make further comment, but said he would speak to the press later Thursday in Seoul, capital of South Korea.

Jong Tae Yang, vice-director of America Bureau of the DPRK Foreign Ministry, was in the airport to see off the envoy.

According to U.S. officials, the trip of Bosworth, who arrived in Pyongyang on Tuesday, aimed to bring the DPRK back to the stalled six-party talks on the nuclear issue of the Korean Peninsula.

During his stay, Bosworth held closed-door meetings with DPRK officials, but there had been no information on the outcome of the talks.

The talks were the first bilateral contact between the two sides since U.S. President Barack Obama took office in January this year.

Following his trip to Pyongyang, Bosworth is scheduled to return to Seoul, then travel on to Beijing, Tokyo and Moscow before flying back to the United States next week, according to the U.S. State Department.

The DPRK shut down the Yongbyon nuclear facility in 2007 under a six-nation nuclear disarmament deal. In April this year, it quit the forum and announced it was resuming the reprocessing of plutonium from spent fuel rods at the reactor there.

It carried out its second atomic weapons test in May, and has said it is in the final phase of an experimental highly enriched uranium program -- another way to make an atomic bomb.

The DPRK has expressed willingness to return to the six-party forum but only if it holds satisfactory talks with Washington first.