The time is not right for a planned trip to Pyongyang by Google Executive Chairman Eric Schmidt and New Mexico's former governor Bill Richardson, the United States State Department said on Thursday.

"Frankly, we don't think the timing of this is particularly helpful, but they are private citizens, and they are making their own decisions," said State Department spokeswoman Victoria Nuland at a news conference.

The trip is ill-timed in light of the recent rocket launch by the Democratic People's Republic of Korea, she added.