China and the Philippines traded accusations on Sunday over the collision in disputed waters of the South China Sea, as Chinese vessels blocked Philippine boats supplying forces there in the latest of a series of maritime confrontations.

In a statement on Sunday, the U.S. State Department said China's coast guard had "violated international law by intentionally interfering with the Philippine vessels' exercise of high seas freedom of navigation".

On Monday, China foreign ministry spokesperson Mao Ning told reporters that the United States "issued a statement in violation of international law, groundlessly attacking and accusing China's legitimate rights and law enforcement actions".

Mao said the area of the Second Thomas Shoal has always been China's territory.

"Renai Reef is an inseparable part of China's Nansha Islands geographically, economically, politically and historically," Mao said, referring to the names of the Second Thomas Shoal and Spratly Islands by their Chinese names.

Maritime confrontations between Manila and Beijing have become a regular feature in the South China Sea, as both countries assert their territorial claims in the highly strategic waters.

(Reporting by Liz Lee; Writing by Bernard Orr; Editing by Christopher Cushing and Miral Fahmy)