TOKYO (AP) — Japanese, U.S. and South Korean coast guard vessels conducted their first three-way drill on Thursday off Japan's coast as the countries strengthen their maritime ties in response to increased assertiveness by China in pressing its territorial claims.

Skirmishes between Chinese and Philippine coast guard vessels have escalated in the South China Sea, triggering fears that the disputes could escalate to an armed conflict between China and the United States, a longtime ally of the Philippines.

Thursday’s joint drill followed an agreement by the leaders of the three countries last August to enhance security cooperation to safeguard peace and stability in the Indo-Pacific.

Patrol vessels from each country and two helicopters joined search and rescue operations in waters off the northern coast of Maizuru in Kyoto prefecture, based on a scenario of rescuing crew members from a South Korean ship that caught fire after colliding with another boat, the Japanese coast guard said.

Japan in recent years has significantly reinforced its defenses in southwestern Japan, including Okinawa and its outer islands that are considered strategically key in response to growing Chinese assertiveness and tensions around Taiwan, a self-governed island claimed by Beijing.

Coast guards from Japan, the United States and South Korea signed an agreement last month to work together to preserve maritime resources, counter illegal fishing, conduct search and rescue operations and improve maritime law enforcement capabilities in the region.

China routinely sends coast guard vessels into waters surrounding disputed islands controlled by Japan.