China has refused repeated U.S. requests to eliminate export restraints on rare earths that have created concern among its trading partners, the U.S. Trade Representative's office said Thursday.

"Going forward, the United States will continue to pursue vigorous engagement with China on this issue and will not hesitate to take further action, including WTO dispute settlement, if appropriate," USTR said in an annual report on how well China has complied with commitments it made when it joined the World Trade Organization in 2001.

The warning came one day after USTR said it had begun a legal challenge at the WTO against certain Chinese subsidies for wind power equipment manufacturers.

U.S. officials said on Wednesday they could file additional cases against China, and the new report amplifies U.S. concerns over China's export restrictions on rare earths.

It said the United States most recently pressed China to eliminate its export restraints on rare earths during the high-level U.S.-China Joint Commission on Commerce and Trade meeting last week in Washington.

"But to date China has not been willing to change its policies," USTR said.

The annual report, which is required under U.S. law and runs 124 pages, also said China still has not fully implemented some important market-opening commitments it made when it joined the WTO in 2001.

"Frequently, these problems can be traced to China's pursuit of industrial policies that rely on excessive, trade-distorting government intervention intended to promote or protect China's domestic industries and state-owned enterprises," USTR said.