“All of the trends are in the wrong direction, and prospects of resolution are diminishing,” said the report, titled “Stirring Up the South China Sea: Regional Responses.”

The pessimistic conclusion came a day after China stepped up its political and military control of the Paracel and Spratly Islands, which both Vietnam and the Philippines claim, and the Macclesfield Bank, claimed by the Philippines. The islands are known in Chinese as Xisha, Nansha and Zhongsha.

On Monday, the Philippine president, Benigno S. Aquino III, announced plans to buy aircraft, including attack helicopters, that could be used in territorial disputes in the South China Sea. China and the Philippines have competing claims there over the Scarborough Shoal and potentially energy-rich underwater ground around Reed Bank, among other areas.