The US joined the Philippines in a joint exercise in the South China Sea amid rising tensions with China over territorial claim in the area.

The joint exercise included reconnaissance aircraft from the U.S. Navy, as well as the Philippine Air Force’s and the Philippine Coast Guard’s which aims to highlight the right to freedom of navigation and overflight and other internationally lawful uses of the sea as China continues to push for dominance over the area.

At the center of the dispute in the area is China’s controversial nine-dash line, a demarcation used by Beijing to claim the vast majority of the South China Sea—claims that overlap with the exclusive economic zones (EEZs) of several Southeast Asian nations, including the Philippines.

The Permanent Court of Arbitration in The Hague ruled in 2016 that China’s expansive claims have no legal basis under international law, a decision China has rejected.

“Maritime Cooperative Activities help us continue to build strong military-to-military ties with our Philippine Navy allies,” said Vice Adm. Fred Kacher, commander of the U.S. 7th Fleet. “With each iteration, these operations further advance our collective efforts to preserve regional stability in this critical part of the world.”

The U.S. 7th Fleet is the Navy’s largest forward-deployed numbered fleet and regularly works with allies and partners to support a free and open Indo-Pacific.

“The U.S. Coast Guard has a significant presence in the Indo-Pacific region,” added Capt. Brian Krautler, commanding officer of the USCGC Stratton.

“During our Western Pacific deployments, we frequently engage with partner nations through professional exchanges and capacity-building activities, as demonstrated in this operation. It’s an opportunity to reinforce vital ties with our counterparts who share a commitment to maintaining a free, secure, and open maritime environment.”