A Chinese fighter plane had an “unsafe” and “unprofessional” encounter with the US-owned special operations aircraft C-130 last June in the South China Sea, a recently revealed intelligence announced.

“We’ve seen an alarming increase in the number of unsafe aerial intercepts and confrontations at sea by PLA aircraft and vessels,” US Department of Defense (DoD) Secretary Lloyd Austin said. He added that the occurrence made by the Chinese side “should worry us all.”

This incident, which has not been disclosed before, occurred when Chinese aircraft engaged in more offensive military maneuvers in the East and South China seas in previous months, including jets belonging to Australia and Canada. Defense Secretary Lloyd Austin expressed his disapproval of what he called the “behavior” of China in Singapore a month ago.

A Chinese Su-30 and an American C-130 were involved in the incident that occurred in June. Said one of the eyewitnesses, the aircraft that belonged to the US was a special operations forces model of the Lockheed Martin C-130 cargo aircraft. “Our aircrews frequently encounter safe and professional intercepts, and when it is otherwise, we have procedures in place to address it,” said the spokesperson for the Department of Defense, Lt. Col. Martin Meiners, who refused to elaborate on the encounter.