The United States flew a Boeing P-8 surveillance plane over the disputed South China Sea on Saturday, a move that a top U.S. Navy admiral called “routine” to the dismay of China. China argues that such activities cause serious damage to U.S.-China relations, reports Reuters.

On Monday, Navy Adm. Scott Swift, commander of the U.S. Pacific Fleet, confirmed to reporters in Seoul that he had been aboard the seven-hour surveillance flight.

In May, China called a similar surveillance flight carrying CNN employees over the South China Sea “irresponsible and dangerous.”

Adm. Swift reportedly said his flight, like the CNN flight in May, was routine.

“We have forces deployed throughout the region to demonstrate the United States commitment to freedom of navigation,” said the admiral.

The surveillance flight provided him with the opportunity to see “first-hand” new operational capabilities in the fleet, he added.

Adm. Swift described communications with China as “positive and structured.”

“They’re normalized, if you will,” he noted.

However, China’s Defense Ministry reportedly said it was “resolutely opposed” to U.S. surveillance flights, adding that it hoped America did not choose sides in the South China Sea dispute. It is unclear whether or not China warned Adm. Swift’s aircraft away.

“For a long time, U.S. military ships and aircraft have carried out frequent, widespread, close-in surveillance of China, seriously harming bilateral mutual trust and China’s security interests which could easily cause an accident at sea or in the air,” the ministry said in a statement provided to Reuters.

“In a separate statement, China’s Maritime Safety Administration warned ships not to enter waters to the east and southeast of Hainan island from July 22 to July 31 due to military exercises. It gave no other details,” Reuters reports.

China claims ownership of most of the South China Sea, with the Philippines, Vietnam, Malaysia, and others disputing its claim.

“China has almost finished building a 3,000-meter-long (10,000-foot) airstrip on one of its artificial islands in the disputed Spratly archipelago of the South China Sea, according to satellite imagery of the area,” reports Reuters.

“Washington has demanded China halt land reclamation and militarization of the disputed area and to pursue a peaceful resolution according to international law,” it adds.

In May, U.S. Secretary of Defense Ashton Carter declared that the U.S. would not be deterred by China’s activities in the South China Sea.