The Japanese and US military flew a combined fighter jet over the Sea of Japan on Thursday, in apparent retaliation to a joint bomber fly by Russia and China when US President Joe Biden was in Tokyo. The Japan-US joint flight on Wednesday was intended to “confirm combined capabilities of the Japanese SDF and the US forces and to further strengthen the Japan-US alliance,” according to a statement from the Joint Staff of the Japanese Self-Defense Force. “In order to respond to any emergency, we are taking utmost readiness.”

While Biden was meeting with Japanese Prime Minister Fumio Kishida and their counterparts from India and Australia for the Quad, an Indo-Pacific economic and security coalition meant to counter China’s growing influence in the region, Chinese and Russian strategic bombers flew together near Japan on Tuesday, according to Japan’s Defense Ministry.

The mission took place just hours after North Korea launched three missiles, including an intercontinental ballistic missile, into the sea between the Korean Peninsula and Japan, raising fears of another nuclear test by Pyongyang. The rockets landed in waters beyond Japan’s exclusive economic zone.

According to Japanese Defense Minister Nobuo Kishi, Chinese H-6 bombers joined Russian TU-95s over the Sea of Japan and flew to locations over the East China Sea, but did not breach Japanese airspace. A Russian IL-20 surveillance jet was also sighted flying off the northern coast of Japan.