A retired American admiral wants the U.S. military and the Self-Defense Forces to consider joint activities in the South China Sea, where China’s militarization has raised tensions.

In a recent interview, Jonathan Greenert, formerly the top uniformed officer in the U.S. Navy, also urged Southeast Asian nations to weigh the possibility of unified action to deal with the maritime issue more effectively.

“We’re very close allies,” Greenert, who retired as chief of naval operations in September, said, referring to the 1960 bilateral security treaty set up by Japan and the United States.

“Allies should be able to operate wherever they choose,” Greenert said. The U.S. military and the SDF have already conducted joint drills in the South China Sea, and his remarks apparently suggest that this cooperation should extend beyond training.

Until recently, the overseas activities of the SDF had been restricted by Japan’s postwar Constitution, which banned the use of force to settle international disputes under Article 9. But the Abe administration enacted two divisive security laws earlier this year after reinterpreting, rather than formally amending, the supreme code. Now the SDF can theoretically engage in collective self-defense, or coming to the aid of an ally under attack, even when Japan itself is not attacked.

“To say that we are not going to operate in the South China Sea, because ‘China won’t like that,’ to me is not a good idea,” Greenert said.

On the other hand, both the United States and Japan should avoid upsetting China by sailing their naval ships together in the waters without announcing their intent beforehand, Greenert said.

“Maybe the first operation would be humanitarian assistance, disaster relief,” said Greenert, who once commanded the Seventh Fleet, which operated from the Western Pacific to the Indian Ocean.

Washington has criticized Beijing for building airstrips and installing military equipment on contested areas in the South China Sea, ignoring claimants like the Philippines and Vietnam and sending ships into waters China claims as its own.

“China is operating on their own rules and regulations and mandates, and it’s inconsistent with the rest of the world,” Greenert said.

The United States should continue its Freedom of Navigation operations, in which the Navy sends ships within 12 nautical miles (22 km), which defines the limit of territorial waters, of areas China unilaterally claims, he said, noting other countries could join the U.S.-led operation if transparency is ensured.

“We have more tendency of success with a multilateral approach with China,” Greenert said.

Potential participants include the Association of Southeast Asian Nations, or organizations that China is a part of, “where they are confronted with this situation and asked to explain and look for compromise or solutions,” he said.

On the long-delayed plan to move U.S. Marine Corps Air Station Futenma in Okinawa, Greenert said flexibility may be needed for both the U.S. and Japan to resolve the contentious issue.

Now is a great opportunity for the leaders to “maybe revise the plan and realize it’s going to take longer, because there are a lot of local issues that have to be worked through,” he said, referring to fierce residential opposition to the bases.