The U.S. government said it has officially questioned China regarding whether it had a hand in helping North Korea develop long-range ballistic missiles.

State Department spokeswoman Victoria Nuland said during a regular briefing Friday that questions were raised against China as part of discussions regarding North Korea. But she avoided answering questions about China’s response, saying talks were ongoing over the issue.

Ahead of the briefing, United States congressman Mike Turner wrote a letter to Secretary of State Hillary Clinton and Director of National Intelligence James Clapper, urging an investigation into North Korea’s missile development project.

U.S. Secretary of Defense Leon Panetta also said that he was sure that China provided some assistance to North Korea’s missile program without elaborating on it.

He made the comment to members of the House Armed Services Committee on Thursday when asked whether China had been supporting North Korea's missile program through "trade and technology exchanges."