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WASHINGTON (Reuters) - U.S. Defense Secretary Robert Gates expressed concern on Thursday about the increasing sophistication of China’s military and called on Beijing to be more open about its intentions.

Gates said a new annual Pentagon assessment of China’s military, due to be released on Friday, depicts “a country that has steadily devoted increasing resources to their military, that is developing some very sophisticated capabilities.”

“Some of the capabilities that are being developed are of concern,” he told reporters at the Pentagon.

The China Military Power Report issued by the Pentagon last year said China’s buildup retained a long-standing focus on rival Taiwan but that years of double-digit growth in arms spending gave it the ability to project power further afield.

Gates, who has seen the 2007 report, said the new document would not contain “any exaggeration of the threat” and reiterated a long-held U.S. call for greater Chinese transparency about its intentions and strategies.

“These are assessments that are in this publication,” he said. “It would be nice to hear first-hand from the Chinese how they view some of these things.”

Chinese President Hu Jintao said on Wednesday his country must build up more modern armed forces to safeguard national security, according to the official Xinhua news agency.

The expansion of China’s navy includes a growing submarine fleet and new ships suitable for the open seas, fueling fears in the United States that its military could alter the balance of power in Asia.

China has said it would attack Taiwan if the self-ruled island, which Beijing views as a renegade province, formally declares independence.