Google chairman Eric Schmidt told North Korean officials their country would never develop unless it embraced Internet freedom, he said on Thursday as he returned from a visit to Pyongyang.

Former US ambassador to the United Nations Bill Richardson, who led the trip, urged North Korea to adopt a moratorium on ballistic missiles and nuclear tests following the communist state's widely criticised rocket launch last month.

Schmidt said he told North Korean officials they should open up the country's Internet "or they will remain behind".

"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, and it will make it harder for them to catch up economically," he said.

"Once the Internet starts, citizens in a country can certainly build on top of it. The government has to do something. It has to make it possible for people to use the Internet which the government in North Korea has not yet done."

Richardson, also a former governor of New Mexico, said: "We strongly urged the North Koreans to proceed with a moratorium on ballistic missiles and possible nuclear test."

The pair told reporters at Beijing airport that they did not meet North Korean leader Kim Jong-Un on the trip, or US citizen Kenneth Bae.

Bae was arrested in November after entering the country as a tourist, according to the North's official news agency, which said he had admitted committing a crime against the state.