Japan and China are accusing each other of violating the airspace around the Japanese-controlled East China Sea islands that Beijing also claims.

Japan’s Foreign Ministry issued a statement saying that it has protested to Beijing after a Chinese helicopter that took off from one of China’s four coast guard boats had entered Japan’s territorial waters around the Senkaku island, violating the Japanese airspace around them for about 15 minutes on Saturday.

In response to the airspace intrusion, Japan’s Self-Defense Force scrambled fighter jets, the Defense Ministry said.

China routinely sends coast guard vessels and aircraft into waters and airspace surrounding the islands, which China calls the Diaoyu, to harass Japanese vessels in the area and force Japan to scramble jets in response.

The latest territorial flap comes as Japan and China were appearing to have warm ties as both countries seek to mitigate damages from the U.S. tariff war.

The Japanese Foreign Ministry said it lodged a “very severe protest” through the Chinese embassy in Japan, claiming that China Coast Guard actions infringed Japan’s sovereignty and urging the Chinese government to ensure preventive measures.