BEIJING — The disputes between China and four of its Southeast Asian neighbors over claims in the South China Sea have become so intense, the prospect of open conflict is becoming more likely, an authoritative new report says.

The disputes, enmeshed in the competition for energy resources, have reached an impasse, according to the report, by the International Crisis Group, a research organization that has become a leading authority on the frictions.

“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.