Over the weekend, China’s military released photographs of its heavily armed fighter aircraft training, it said, over the South China Sea, and claimed they flew out of an unnamed airstrip in those contested waters. The Chinese did not give the specific site, but the runway is believed to be on Woody (Yongxing) Island, according to the South China Morning Post.

It was the latest reaction to last week’s freedom of navigation exercise conducted by the USS Lassen , one of the U.S. Navy’s guided-missile destroyers. The Lassen , watched by American reconnaissance aircraft off in the distance, sailed within 12 nautical miles of Subi and Mischief Reefs in the Spratly chain of rocks, reefs, and islets in the South China Sea—waters claimed by Beijing.

And it comes after a menacing statement by the chief of China’s navy, who raised the specter of open war with the United States in a way that can only be construed as a threat.

“If the United States continues with these kinds of dangerous, provocative acts, there could well be a seriously pressing situation between frontline forces from both sides on the sea and in the air, or even a minor incident that sparks war,” said Admiral Wu Shengli, according to Reuters.

In case you have missed the buildup to this dangerous moment, Beijing has been building what is now known as “the great wall of sand” by dredging and filling around rocks and reefs also claimed by other countries, turning them into artificial islands and potential military bases. That appears to be the purpose China’s People’s Liberation Army Navy intends for Subi and Mischief.

China, Taiwan, the Philippines, and Vietnam maintain competing claims to the two reefs. Both features are far closer to the Philippines than China, but Beijing believes it has sovereignty nonetheless.

In fact, Beijing has issued maps showing a huge swath of water—the outlines look like a “cow’s tongue”—where China claims most every reef, shoal, and island. The tongue encloses about 85 percent of the South China Sea, and Beijing appears to take the position that the water inside the line is thus internal Chinese territorial sea.

China’s outsized claims do not sit well, of course, with other countries on the littoral. Washington, for its part, insists that China settle sovereignty disputes peacefully. More important, Washington also insists, as it does in all other parts of the world, that coastal states like China not infringe on freedom of navigation, the right to use international water and airspace. Apart from China, every nation recognizes that the South China Sea is part of the global commons.

When the Lassen set its course to assert and preserve that freedom, Beijing was enraged and Admiral Wu’s war talk began.

China’s defenders pointed out that official media did not quote Admiral Wu as raising the possibility of war, and in a narrow sense the defenders are right. People’s Daily, the self-described mouthpiece of the Communist Party and therefore China’s most authoritative publication, used “accidental conflicts” in its English online edition. State media did not use the Chinese character for “war” when summarizing Wu’s remarks.

But Wu’s words were not a mere observation. They were, in the context in which they were delivered, a promise.

Remember, the Lassen was sailing in international waters. Neither the UN Convention on the Law of the Sea, which China ratified in 1996, nor customary international law gives reclaimed features like Subi and Mischief a 12-nautical mile band of territorial water.

And even if these features were entitled to such a band, the Lassen was entitled to sail within 12 miles of them because of the concept of “innocent passage.”

“There is not the slightest merit to China’s legal position,” James Holmes of the Naval War College told The Daily Beast on Saturday.

China’s position is all the more incredible because in early September five Chinese warships sailed within 12 nautical miles of one of the Aleutians, obviously claiming innocent passage, and there was no protest from the Pentagon.

So whatever translation of Wu’s words one accepts, why would there be an “accident” or “conflict” just because an American vessel was transiting international water on the same principle Chinese ships used to sail inside American waters a few weeks before?

We do not have to speculate as to Wu’s meaning, in fact. On Friday, the official China Daily settled the issue with this ominous-sounding headline: “Military Keeping ‘All Options Open’: Navy Chief.” Using the code words for military action, state media effectively confirmed Wu had in fact threatened war with his use of “accidental conflicts.”

As Holmes, the co-author of Red Star Over the Pacific, puts it, “Wu sounds like a Rhode Island mobster: ‘Nice ship there, U.S. Navy, sure would be a shame if something happened to it.’”

Richard Fisher, military analyst at the International Assessment and Strategy Center, notes that Wu’s words were “official.” “As he gave a formal press conference,” Fisher wrote in an email to The Daily Beast over the weekend, “Admiral Wu’s threat would have to have had the highest level of approval from the Chinese Communist Party leadership.”

Wu’s warning was delivered directly to his American counterpart, Chief of Naval Operations Admiral John Richardson, during a video teleconference, so it’s clear the American Navy heard it loud and clear. And then the Chinese, with a barrage of state media articles, made sure the rest of the world heard it, too. So Wu’s words raised the stakes everywhere, not just the vitally important South China Sea, where each year $5.3 trillion in commerce transits.

“If China gets away with it, there’s no reason in principle that others couldn’t assert title to marginal seas elsewhere on the map,” Holmes notes. The international community, therefore, cannot afford to let Beijing close off the South China Sea.

That Beijing would try to do such a thing seems, at first glance, inconceivable, but China has shown it is willing to use force to get its way in that body of water. It has twice fought Vietnam to grab territory. Moreover, it seized Mischief Reef in 1994 from the Philippines, and it took Scarborough Shoal from Manila in 2012. Now it is moving with determination to grab Second Thomas Shoal, trying to force out a handful of Philippine marines sitting on a ship marooned on that feature as a marker of Manila’s sovereignty.

“Ten years ago, the People’s Liberation Army Navy would never have publicly challenged the U.S. Navy, either with aggressive rhetoric, as Admiral Wu Shengli has done, or with aggressive tactical actions, as he is threatening to do,” Chris Harmer of the Institute for the Study of War told The Daily Beast. Yet the Chinese think they can now intimidate Washington.

Up to now, an expansionist Beijing has only picked on smaller nations like the Philippines, but today China apparently thinks it is strong enough to take on the United States. So the Chinese are both arrogant and aggressive, and that is one particularly frightening combination.