The U.S. special representative arrived in South Korea after completing his three-day trip to the Communist country, the first such bilateral meeting between North Korea and the United States since President Barack Obama took office.
"It was a very useful set of meetings," Bosworth told China's official news agency Xinhua before departing Pyongyang.
Although North Korea had been insisting on the bilateral talks, the official U.S. position had been that Bosworth's mission was only to persuade Pyongyang to return to the six-nation talks on the North's nuclear disarmament. The talks among the United States, China, Russia, the two Koreans and Japan remain stalled after Pyongyang pulled out following U.N. condemnation of the North's nuclear and missile tests earlier this year and the tightening of sanctions.
The Xinhua report said Bosworth declined to make additional comments, adding he would speak to the media after reaching Seoul.
After Seoul, Bosworth is scheduled to travel to Beijing, Tokyo and Moscow before returning to the United States, the report said.
The South Korean news agency Yonhap quoted a South Korean Foreign Ministry official as saying: "Special representative Bosworth visited North Korea at a time when the six-way talks are in a protracted deadlock. When the veteran diplomat used the words 'very useful,' he appears to have signaled progress."
North Korea, which shut down its Yongbyon nuclear facilities in 2007, began reprocessing plutonium at the reactor there after quitting the six-nation talks.