China's military on Monday said a U.S. combat ship illegally entered waters adjacent to the Second Thomas Shoal, a disputed South China Sea atoll.

"The U.S. seriously undermined regional peace and stability," said a spokesperson for China's Southern Theater of Operations in a statement.

The spokesperson also said the U.S. deliberately disrupted the South China Sea and seriously violated China's sovereignty.

(Reporting by Bernard Orr and Shanghai newsroon; Editing by Chizu Nomiyama)