ASPEN, Colo. – The top U.S. military officer in the Pacific sternly warned China on Friday to immediately cease its “aggressive coercive island building” in the South China Sea, which he argued was intended clearly for China’s military use as forward operating bases in combat against their regional neighbors.

Adm. Harry Harris, commander of U.S. Pacific Command, said the U.S. would use military force to defend its interests and its allies against any threats from the islands.

“I believe those facilities are clearly military in nature,” Harris said at the Aspen Security Forum, an annual gathering in Colorado of dozens of top U.S. national security leaders, convened by the Aspen Institute.

In his notably undiplomatic remarks, Harris called on China to show meaningful diplomacy to resolve the territorial disputes. But the four-star admiral also appeared resigned to seeing further construction and eventual deployment of military aircraft and ships.118591

“They are building ports that are deep enough to host warships and they’re building a 10,000-foot runway at Fiery Cross Reef,” Harris said, referring to one of China’s construction activities in the Spratly Islands that Japan has protested. “A 10,000-foot runaway is large enough to take a B-52, almost large enough for the Space Shuttle, and 3,000 feet longer than you need to take off a 747. So, there’s no small airplane that requires a runway of that length. They’re building revetted aircraft hangars at some of the facilities there that are clearly designed, in my view, to host tactical fighter aircraft.”

Harris also said he is concerned the islands could be used as a chain of Chinese listening posts. “Certainly, those islands, which are well out in the South China Sea, extends a surveillance network that could be in place with radars, electronic warfare capabilities and the like.” If that happens, he said, American warships could strike them in combat.

“I think those islands, given the capabilities we have, are clearly and easily targets in any combat scenario with China. But they’re also easily seen as forward operating posts.”

“Any increase of capability like that in that area is cause for concern,” Harris said. The U.S. has not yet seen China place any anti-ship missiles or supporting gear on the islands, he added.

The U.S. commander dismissed Beijing’s repeated claims that the island expansions were rightful and peaceful, and said China has shown no credible diplomatic effort to resolve its territorial disputes with neighboring countries.

“Most countries choose to pursue diplomatic means to address their disputes. China, on the other hand, is changing the status quo in the region through aggressive coercive island building without meaningful diplomatic efforts toward dispute resolution or arbitration,” Harris said, reading opening remarks at his appearance in Aspen. “China is changing facts on the ground…essentially, creating false sovereignty…by building man-made islands on top of coral reefs, rocks, and shoals,” Harris said. “These activities are harming the environment and will not strengthen any country’s legal claims to disputed areas in the South China Sea.

“We call on China to use the mechanisms of international dispute resolution in good faith, and to abide by those decisions as so many of its regional neighbors have already done. China has in the past accused the U.S. of ‘pursuing international hegemony’ and adopting a ‘Cold War mentality’ toward China. Nothing could be further from the truth. It is China’s actions that are inducing its South China Sea neighbors to build stronger relationships with each other and the U.S., driven not by a sudden U.S. effort to increase stability and security within the region, but by China’s conspicuous failure to do the same.”

Earlier this year, the U.S. Navy released video taken by its maritime patrol aircraft of Chinese construction crews expanding reefs and building an airbase in the Spratlys.