Two Chinese J-10 fighter jets have intercepted a U.S. Navy surveillance plane in an “unsafe” and “unprofessional” manner in international airspace over the East China Sea, the Pentagon said Monday, in the latest such incident involving the two militaries.

“On July 23 EDT, two Chinese J-10 aircraft intercepted a U.S. Navy P-3 operating in international airspace in the East China Sea,” U.S. Defense Department spokesman Lt. Col. Christopher Logan told The Japan Times in an email.

“The aircrew deemed the intercept unsafe and unprofessional,” Logan said. “Operations were able to continue unimpeded.”

The Pentagon declined further comment, but both Reuters and Fox News, quoting anonymous U.S. officials, reported that one of the Chinese fighters had maneuvered suddenly, popping up 300 feet (91 meters) in front of the U.S. plane.

Fox News said both Chinese fighters were armed with air-to-air missiles, according to officials.

The encounter was the first incident of its kind since May 24, when two Chinese J-10s intercepted a U.S. surveillance plane in international airspace above the contested South China Sea.

Media reports at the time said that U.S. surveillance plane was in international airspace about 150 miles (240 km) southeast of China’s Hainan Island, home to a sprawling Chinese submarine base.

One of the Chinese fighters in the May incident reportedly flew about 200 yards (180 meters) in front of the U.S. aircraft and about 100 yards above it, doing slow turns.

U.S. military reconnaissance flights near China’s coastline and in the South China Sea have angered Beijing as it seeks to reinforce effective control of much of the strategic waterway, through which $5 trillion in trade passes each year. The Philippines, Vietnam, Malaysia, Taiwan and Brunei also have overlapping claims.

Just a week prior to the South China Sea encounter, the U.S. said that two Chinese Su-30 fighter jets had intercepted a U.S. radiation-detecting plane in international airspace over the Yellow Sea off the Korean Peninsula.

Beijing has blamed the close encounters on U.S. planes and ships that it says frequently conduct surveillance “near Chinese territory.”

The East China Sea, where Beijing is embroiled in a dispute with Tokyo over the Japanese-controlled Senkaku Islands, known in China as the Diaoyus, has seen an uptick in similar incidents — including dangerous encounters between Chinese military aircraft and Air Self-Defense Force fighter jets.

China’s military has also ramped up its training flights through key entryways into the western Pacific Ocean near Japanese territory.

Earlier this month, Chinese Air Force bombers conducted long-range drills over the Bashi Channel and the Miyako Strait “several times,” with the country’s Defense Ministry urging Japan to “get used to” the military exercises.