China and Russia conducted a joint live-fire naval exercise in Japan’s exclusive economic zone using machine guns, Tokyo announced on Tuesday.

Japan described the exercise as evidence that the Chinese and Russian militaries are “strengthening their cooperation,” according to the country’s top government spokesperson, Minoru Kihara.

The incident happened 180 kilometers southwest of Okinotori Island, which Japan considers its southernmost island. This claim is disputed by South Korea, Taiwan, and China, who consider Okinotori a rock that therefore does not have exclusive economic zone status. Japan warned China that the drill “could have endangered the navigation of nearby ships.”

China’s foreign ministry spokesperson Lin Jian dismissed Tokyo’s concerns, suggesting China had carried out “legitimate and lawful activities” and that Tokyo was “exaggerating external threats.”

Relations between China and Japan have worsened since Prime Minister Sanae Takaichi claimed Japan could militarily defend Taiwan, which China considers its territory, in the event of a conflict or blockade. Japan has increasingly moved away from its post-World War II peaceful position toward a more proactive defense policy.

China and Russia conducted another joint naval exercise earlier this month, after flying bombers over waters surrounding Japan in June. Japanese and Chinese coast guards also faced off near disputed islands this month, with each claiming the other’s vessels violated its territorial waters.

On Monday, the United States condemned what it called “dangerous and aggressive” action by China in the South China Sea, where Chinese personnel clashed with Filipino sailors at a disputed shoal.

“China’s troubling pattern of provocation against lawful Philippine maritime operations undermines regional peace and stability and directly contradicts China’s repeated commitments to resolve disputes peacefully,” State Department spokesman Tommy Pigott said.