LADD REEF, SOUTH CHINA SEA — Satellite images taken by a U.S. based firm revealed suspected dredging work on Ladd Reef, a coral reef controlled by Vietnam in the South China Sea.

Ladd Reef is about 450 km from Vietnam’s southeastern coast and is completely submerged at high tide. It has a 42-meter-tall lighthouse, which is operated by a small number of Vietnam soldiers and worker.

Analysts told Reuters that such dredging work could be the precursor to more extensive construction on other reefs, and Ladd Reef might be used to boost access for supply ships and fishing boats. It could also help defend the nearby Spratly Islands, where Vietnam has expanded its airstrip.

Vietnam is one of the many nations that claims the South China Sea as part of its territory. China, the Philippines, Malaysia, Brunei and Taiwan have also made claims in the region. Vietnam has become China’s main rival in the disputed South China Sea. According to Reuters, the mobile rocket launchers installed on several islands controlled by Vietnam are capable of striking China’s runway and military installations.