The Japanese government's bid to "nationalize" the Diaoyu Islands had broken its consensus with China to shelve the territorial dispute, a U.S. expert said Thursday.

"First of all, I think that Japan's actions have been key in explaining what China has done," said Kenneth Lieberthal, a senior fellow at the Brookings Institution who had been the senior director for Asia at the National Security Council in the Clinton administration.

Speaking at a symposium at the Washington-based think tank, he also admitted it was a "huge mistake" when U.S. government officials made comments that suggested Washington did have a position on the dispute.

"I think that does us no good. And occasionally, some comments like that have come out," Lieberthal said. "I think that they are regrettable."