China’s plans to build up a disputed island near the Philippines could lead to a regional conflict, Defense Secretary Ash Carter told Congress on Thursday.

Carter was asked about the strategic significance of China’s plan to add military facilities to a disputed island known as Scarborough Shoal located about 120 miles—within missile range—of Subic Bay, Philippines, where U.S. warships will be based.

The defense secretary said Scarborough is “a piece of disputed territory that, like other disputes in that region, has the potential to lead to military conflict.”

“That’s particularly concerning to us, given its proximity to the Philippines,” Carter told a Senate Armed Services Committee hearing on efforts to counter the Islamic State terrorist group.

Carter said the Pentagon has similar views about a number of island disputes in the South China Sea, where China has been claiming most of the sea as its maritime territory and demanding that other states, including the United States, keep out of the region.

The comments came in response to questions posed by Sen. Dan Sullivan (R., Alaska) who revealed during the hearing that Scarborough is the third vertex of a triangle of Chinese military bases that could be used to threaten the main Philippines island of Luzon.

A map showed Woody Island in the Paracels and three other islands in the Spratlys Islands that are undergoing militarization by the Chinese as part of the island building program.

Pentagon Warns of Conflict Over Chinese Buildup on Disputed Island