The State Department said Friday China recently denied a request from a U.S. aircraft carrier for a port visit in Hong Kong, in an apparent sign of mounting tension in the disputed South China Sea.

Defense Chief Ash Carter and his Philippine counterpart visited the carrier, the USS John C. Stennis, in those waters two weeks ago. Experts told the South China Morning Post that move likely irked Beijing.

Gabrielle Price, a spokeswoman for East Asia, said the department was informed that a request for visit by the USS Stennis and accompanying vessels were denied. Price said that the U.S. has a history of successful port visits and it expects that will continue.

The Hong Kong-based South China Morning Post quoted China's Foreign Ministry as saying that port calls by U.S. warships were examined on a "case by case basis."

The U.S. Pacific Command revealed last week that it had sent six A-10 Thunderbolt aircrafts near the China-claimed Scarborough Shoal, according to the Morning Post. China had expressed concern about those moves.

The Associated Press contributed to this report.