On Tuesday, Russian and Chinese military planes conducted joint exercises to patrol the Asia-Pacific region, Russia’s defense ministry said in a farewell statement to U.S. Vice President Joe Biden during his Asia visit that enraged Beijing.

The defense ministry said Russian Tu-95 strategic bombers and Chinese Xian H-6 jets took part in the joint patrol over the Japanese and East China seas.

According to a U.S. official, the exercise revealed the depth of cooperation between Japan and the United States.

During part of the exercise, Japanese and South Korean aircraft shadowed the Russian and Chinese aircraft.

Russia and China approached Japan’s airspace, prompting Japan to scramble jets. Nobuo Kishi said this occurred when the leaders of the Quad – a group of countries including the United States – were in Tokyo.

Kishi said Tokyo had voiced “grave concerns” to Russia and China at a news conference.

According to him, Beijing and Moscow are likely to have provoked the incident, which occurred on the same day that Vice President Biden, Indian Prime Minister Narendra Modi, and Australia’s newly elected leader, Anthony Albanese, met in Tokyo.