The U.S. Department of Defense (DOD) confirmed that Beijing has installed military equipment capable of jamming communications and radars on two of its outposts in the South China Sea’s Spratly Islands, reports the Wall Street Journal (WSJ), citing a satellite image and U.S. officials.

“China has deployed military jamming equipment to its Spratly Island outposts,” an anonymous DOD official told the Journal.

Citing U.S. officials, WSJ describes the move as “a significant step in [China’s] creeping militarization of the South China Sea.”

“While China has maintained that the construction of the [artificial] islands [on the South China Sea] is to ensure safety at sea, navigation assistance, search and rescue, fisheries protection and other nonmilitary functions, electronic-jamming equipment is only for military use,” the DOD official noted.

A photo taken by the commercial satellite company DigitalGlobe in March and obtained by the Journal supports the revelation that China installed military jamming equipment on the Fiery Cross Reef and Mischief Reef of the Spratly Islands over the last 90 days.

Referring to the satellite picture, WSJ notes:

It shows a suspected jammer system with its antenna extended on Mischief Reef, one of seven Spratly outcrops where China has built fortified artificial islands since 2014, moving sand onto rocks and reefs and paving them over with concrete.

Drawing the ire of the United States and countries in the region, China has constructed artificial islands on the South China Sea capable of housing military installations.

“China has built a massive infrastructure specifically — and solely — to support advanced military capabilities that can deploy to the bases on short notice,” Adm. Harry Harris, the head of the U.S. Pacific Command, told lawmakers last month, adding:

In 2017, China took significant steps to further militarize its bases on disputed features [in the South China Sea] … The U.S. takes no position on competing sovereignty claims to naturally formed islands in the South China Sea, but we do strongly call on all countries to ensure their claims and activities are consistent with international law.

China’s “impressive military buildup” over the last years may soon enable the People’s Liberation Army (PLA) to challenge America’s military dominance in the Pacific region “across almost all domains,” the American commander warned.

WSJ reports:

While Chinese military personnel are at the Spratly outposts and Chinese ships dock there, China has yet to station ground units or fighter planes on the artificial islands, U.S. officials say. Nor have surface-to-air missiles or anti-ship cruise missiles been deployed in the Spratlys, though spots to install such weapons have been prepared, U.S. officials said.

But China’s ability to quickly shift military assets to the outposts is a serious concern for the Pentagon since it could enable China to control vital trade routes, exclude other claimants from disputed areas and interfere with the U.S. military’s plans to defend Taiwan.

China claims “indisputable” ownership over all South China Sea islands and their adjacent waters. Beijing’s claims impact the territorial integrity of the other sovereign states in the region, namely Taiwan, Brunei, the Philippines, Malaysia, Vietnam, and Indonesia.

Already, “three of [China’s] outposts in the Spratlys—Fiery Cross Reef, Mischief Reef, and Subi Reef—now feature 10,000-foot runways, hangars for fighter planes, ammunition bunkers, barracks and deep-water piers for ships,” notes the Journal.