MANILA, Philippines — The Philippines has protested China’s deployment of what Manila describes as a floating “structure” with personnel on a disputed shoal in the South China Sea, fearing it could be a part of Beijing’s effort to turn the uninhabited atoll into an island base, Philippine officials said Tuesday.

The Department of Foreign Affairs said, without elaborating, that it lodged a protest over China’s latest action on the Scarborough Shoal, which was spotted by the Philippine military and coast guard.

China dismissed Manila’s concern and reiterated that it has “indisputable sovereignty” over the shoal and adjacent waters, without responding or offering any details to the Philippine officials.

“Any activities China conducts on Huangyan Island, including scientific research, are the legitimate rights of a sovereign state,” Ministry of Foreign Affairs spokesperson Lin Jian said in Beijing.

“China urges the Philippine side to cease maritime infringements and provocations and stop hyping up the issue,” he added.

China deployed ships to guard the uninhabited Scarborough in 2012, after weeks of a tense standoff with Philippine ships, prompting Manila to bring its disputes with Beijing to international arbitration, which the Philippines largely won.

Citing the 1982 U.N. Convention on the Law of the Sea, the 2016 arbitration ruling invalidated China’s claims to virtually the entire South China Sea.

China, however, refused to participate in the arbitration initiated by the Philippines and dismissed the ruling as a sham, claiming it was concocted by the United States with the Philippines.

More than a decade ago, China started transforming disputed and uninhabited reefs into what are now missile-protected island bases — including three with military-grade runways — in the Spratlys archipelago, a fiercely disputed area in the South China Sea.

In the mid-1990s, Chinese forces seized one of the seven areas, the Mischief Reef, by erecting small huts on stilts and saying at the time that they would serve as fishermen’s shelters in the high seas.

The Philippines strongly protested China’s seizure of Mischief, saying the area lies within its internationally recognized exclusive economic zone.

The chief of staff of the Armed Forces of the Philippines, Gen. Romeo Brawner, said the Philippine military will not allow China to turn Scarborough into another island base.

“We will not allow an incident before to happen again, where a small structure was built and later on, it grew into an artificial island,” Brawner said.

Vietnam, Malaysia, Brunei and Taiwan also lay claim to the South China Sea, but territorial clashes have particularly spiked between Chinese and Philippine coast guard and navy forces in recent years.

The U.S. has repeatedly warned that it is obligated to defend the Philippines, its oldest treaty ally in Asia, should Filipino forces, ships and aircraft come under an armed attack, including in disputed waters.