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.