CNN broadcast an exclusive report, as one of its reporters hitched a ride on a U.S. Navy P-8 patrol aircraft overflying the artificial islands the People’s Republic of China (PRC) is building in the South China Sea. The Chinese repeatedly tried to warn off the aircraft, in English language broadcasts that CNN included in its report.

The report confirms that the Chinese are trying to establish sovereignty claims over these areas of the South China Sea by building major artificial islands atop reefs (which, by themselves, establish no territorial claims).

But what is surprising is that the U.S. Navy plane is being warned by “the Chinese navy.” Past encounters have typically involved Chinese civilian law enforcement vessels and civilian fishing boats. But the American aircraft was warned off by the Chinese military, making clear that these islands are currently under the jurisdiction and control of the People’s Liberation Army (PLA). In short, Beijing has deployed military forces to these new, artificial islands, and has therefore already militarized these disputes.

Even more surprising is the Chinese warning that the American aircraft is within a “military alert zone.” As of this time, the PRC has not announced the establishment of a formal air defense identification zone (ADIZ) over the South China Sea, as it has over the East China Sea. For the Chinese, then, to warn the U.S. aircraft that it is entering a military alert zone may signal an imminent Chinese decision in this regard, further heightening tensions.

The Chinese broadcasts highlight Beijing’s view that the air and sea-space in these areas are Chinese territory, and are deploying military forces to enforce that claim. Considering the $5.3 trillion in international trade that transits those waters, China’s actions will have an enormous impact globally.