A Chinese Su-27 performed a series of maneuvers apparently designed to intimidate an American J-8 reconnaissance plane in international waters earlier this week.

NPR reports that the P-8 “Poseidon” aircraft was flying off the island of Hainan in the South China Sea on Tuesday, when it was approached by the Russian-made fighter.

The Chinese pilot performed a barrel roll over the P-8 and flew wing-to-wing with the American at a range approaching just 20 feet.

The J-11 is the Chinese version of the Russian Sukhoi Su-27 “Flanker.” It is a twin-engine super-maneuverable fighter that debuted in the Soviet Air Force in 1985 and remains one of the most advanced fighters in the world. It’s closest American counterpart is the F-15 “Eagle.”

Pentagon Press Secretary Rear Adm. John Kirby voiced his concern about the incident when talking to reporters.

“We have registered our strong concerns to the Chinese about the unsafe and unprofessional intercept, which posed a risk to the safety and the well-being of the air crew and was inconsistent with customary international law,” Kirby said, calling the altercation “very, very close, very dangerous” and saying that “it undermines efforts to continue developing military-to-military relations with the Chinese military.”

The Pentagon also called the interception the most dangerous aerial encounter with a Chinese aircraft since the April 2011 mid-air collision of a Lockheed EP-3 with a Chinese J-8 interceptor.