The Pentagon is reviewing an unsafe encounter between a People’s Liberation Army and U.S. Navy surveillance aircraft over the South China Sea, a defense official told USNI News on Friday.

The Wednesday encounter between a Navy P-3C Orion the PLA KJ-200 was deemed “unsafe” according to a statement from U.S. Pacific Command.

“The U.S. Navy P-3C was on a routine mission operating in accordance with international law,” read the statement.

“The Department of Defense and U.S. Pacific Command are always concerned about unsafe interactions with any Chinese military forces.”

The Pentagon is now reviewing the encounter, Pentagon spokesman Cmdr. Gary Ross told USNI News on Friday.

“Both sides have made considerable efforts to ensure safe operations between ships and aircraft. We have robust communication channels to discuss encounters with the Chinese military, such as the Military Maritime Consultative Agreement mechanism,” he said.

“The Department of Defense will address the issue with China in appropriate diplomatic and military channels.”

The KJ-200, “is used by both the People’s Liberation Army Air Force and the air arm of the People’s Liberation Army Navy, or PLAN, to provide air surveillance,” according to a report in Defense News.

“It is unclear to which branch of China’s armed forces the aircraft involved in this latest encounter belongs, although PLAN KJ-200s have been known to operate from air bases on China’s southern Hainan Island, 530 miles from Scarborough Shoal.”

Unlike other encounters in which PLA aircraft have flown aggressively against U.S. surveillance aircraft – for example a PLA fighter harassed a Navy P-8A Poseidon in 2014 – the incident may have been inadvertent.

The P-3C was in the midst of a turn when the crew received a potential collision alert, spotted the KJ-200 and took evasive action to avoid a crash, one defense official told USNI News on Friday.

The official said it was possible neither aircraft crews knew the other was there until the collision alarm.

The KJ-200, “is used by both the People’s Liberation Army Air Force and the air arm of the People’s Liberation Army Navy, or PLAN, to provide air surveillance,” according to a report in Defense News