The US military is saying that China has installed equipment on islands in the South China Sea capable of jamming communications and radar systems, according to a report on Monday.

The Wall Street Journal, which first reported the development, also cited US intelligence sources as saying the equipment was deployed within the last several months.

“While China has maintained that the construction of the islands 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,” a US Defense Department official said.

The assertion is in line with US Pacific Command chief Admiral Harry Harris’ comments last month to the Senate Armed Services Committee that the infrastructure on the islands is intended “solely” to support advanced military capabilities “that can deploy to the bases on short notice.”

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The alleged military developments come as both the United States and China have been conducting military exercises in the region, though China played down the movements of its Liaoning aircraft carrier strike group in the region.

US officials described the exercise off of Hainan Island as the largest to date in the South China Sea conducted by China. But Chinese news media said the exercise was an attempt to address multiple flaws and deficiencies in the carrier, not show off its advanced capabilities.

Meanwhile, America’s Theodore Roosevelt Nimitz-class carrier strike group was said last week to be traveling to the center of the South China Sea along with warships from allies, following a port visit in Singapore.