BEIJING: Former New Mexico governor Bill Richardson and Google Executive Chairman Eric Schmidt failed to secure the release of a Korean-American held in North Korea during a controversial trip to the secretive state that ended on Thursday.

Richardson told a media briefing at Beijing's airport he was unable to meet Korean-American Kenneth Bae, a 44-year-old tourist who was detained late last year and has been charged with unspecified crimes against the state.

Richardson said he was told that judicial proceedings against Bae would start soon, although he gave no details. North Korean authorities assured him of Bae's good health, he said.

"That is encouraging," Richardson said of Bae's condition, adding he was also given permission to "proceed with a letter from his son, and that will happen shortly".

It was unclear if Richardson had left such a letter with North Korean authorities or if it would be sent later. Bae is being held in a location far from Pyongyang, Richardson said.

The timing of the trip by Schmidt and Richardson was criticised by the U.S. State Department. It came after North Korea carried out a long-range rocket launch last month, which Washington considers a provocative test of ballistic missile technology.

Schmidt said his visit to Pyongyang was private and was to talk about a free and open Internet.

"As the world becomes increasingly connected, their decision to be virtually isolated is very much going to affect their physical world, their economic growth and so forth", Schmidt said in brief remarks.

"The technology in North Korea is very limited," Schmidt said, with a 3G cellphone network for about a million phones run by Egypt's Orascom Telecom Media and Technology Holding SAE that does not support the Internet.

Access to the Internet is available to the government, the military and to universities but not the general public and users are supervised, he said.

"The government has to do something. They have to make it possible for people to use the Internet", he said. "It's their choice now, and time, in my view, for them to start or they will remain behind."

"They showed up and listened to us and asked us a lot of questions", he said.

There was no immediate comment from North Korea about the visit by Richardson and Schmidt other than a report on the official KCNA news agency to say the delegation had left. The trip was met with scepticism across the border in South Korea.

"It wasn't productive on humanitarian grounds", said Chang Yong-seok, a senior researcher at the Institute for Peace and Unification Studies at Seoul National University.

The trip came as the United States, South Korea, Japan and their European allies were pushing at the United Nations to expand long-standing U.N. Security Council sanctions on North Korea after the North's Dec. 12 rocket launch.

Richardson said the North Koreans he met, including a vice foreign minister and other foreign ministry officials, maintained their missile activity was scientific and peaceful.

"I must say I personally disagree", said Richardson, a former U.S. ambassador to the United Nations. "I don't think it is science-based, and it is a violation of the United Nations moratorium."

Pyongyang, according to satellite imagery, is continuing work on its nuclear testing facilities, potentially paving the way for a third nuclear bomb test.

Chang said North Korea would not be budged easily.

"It is possible North Korea will take action after watching to see if the United States changes its policy", Chang said. "It tells us that North Korea is confident and not in a rush; it is going on its own way unyieldingly."

Tensions on the tinderbox Korean peninsula could be reduced following the election of new leaders in South Korea, Japan, and a new secretary of state in the United States, Richardson said.

"The North Koreans were encouraged by the recent statements of the new south Korean president", he said, referring to President-elect Park Gyeun-hye.