WASHINGTON – The commander of the Maritime Self-Defense Force has warned that all of the South China Sea could be “covered by China’s sphere of military influence” if Beijing uses artificial islands it has built there for military purposes.

In a speech Wednesday at a think tank in Washington, Adm. Tomohisa Takei underlined the importance of ensuring that the South China Sea remains “free and open waters” so that the Indian-Pacific area is an “Ocean of Prosperity.”

Should the freedom of navigation be threatened, Takei said that “an unexpected incident at sea can occur as a result.”

China claims most of the South China Sea, believed to be rich in oil and natural gas deposits, despite overlapping sovereignty claims by Vietnam, the Philippines, Brunei, Malaysia and Taiwan.

Japan is not a claimant but has been critical of Beijing’s muscle-flexing in the South China Sea.

“Even though the Indian Ocean and the Western Pacific are geographically separated, they are so closely related that they cannot be separated both politically and economically,” Takei said. “Therefore, we need to regard security in each of these two oceans as identical.”

In a separate think tank meeting, a U.S. government official urged the European Union to speak out more forcefully to support Washington in its dispute with China over the building and militarization of man-made outposts in the South China Sea.

Amy Searight, U.S. deputy assistant secretary of defense for South and Southeast Asia, said Washington welcomed EU calls for a peaceful resolution of territorial disputes in the sea and respect for international law.

But there was “somewhat of a difference of approach” when it came to Washington’s call for a freeze on activity by rival claimants — something China has rejected.

“It would be helpful if the EU would be a little more clear in terms of backing up these principles,” she told a discussion on U.S. and EU policies toward East Asia at Washington’s Center for Strategic and International Studies.

“A little bit more forward-leaning approach that would support, for example, the idea of a halt to further reclamation, further militarization, would be very useful.”

Michael Fuchs, U.S. deputy assistant secretary of state for East Asia, said there was a need to reduce the risks of conflict in the South China Sea, where China has overlapping claims with several states.

“This is about . . . speaking up when we see activity that is concerning,” he said.

David O’Sullivan, EU ambassador to Washington, said the European Union and the United States had very similar objectives, but such statements were a judgment call.

“Completely joining up language is sometimes useful and sometimes counter-productive,” he said.

O’Sullivan said the European Union was concerned about security in East Asia and was adding a security dimension to its work, but made clear there were limits to this.

“The last thing the region needs is more gunboats. I don’t think that’s going to be our contribution to the future security of the region.”