Special to WorldTribune.com

The United States voiced its objection to China’s use of a military plane to land on a South China Sea man-made island in what Beijing claimed was a mission to evacuate three severely ill construction workers.

“We’re aware that a Chinese military aircraft landed at Fiery Cross Reef on Sunday (April 17) in what China described as a humanitarian operation,” Pentagon spokesman Capt. Jeff Davis told CNN. “It is unclear why the Chinese used a military aircraft, as opposed to a civilian one.”

The Chinese military aircraft landed on Yongshu Reef, also known as Fiery Cross Reef, and airlifted the workers to a hospital on Hainan island, according to Xinhua.

The U.S. and several nations disputing China’s actions in the South China Sea have kept a close eye on Fiery Cross Reef in the Spratly Island chain after Beijing constructed a runway long enough to accommodate large military aircraft.

The airstrip, which extends 1.8 miles, was completed this year on reclaimed land around the reef.

“We urge China to reaffirm that it has no plans to deploy or rotate military aircraft at its outposts in the Spratlys, in keeping with China’s prior assurances,” Davis said.

The U.S. has said it will continue to carry out “freedom of navigation” operations in close proximity to the Chinese islands to challenge Beijing’s territorial claims.

During a visit to the Philippines last week, Defense Secretary Ash Carter was aboard the USS John C. Stennis aircraft carrier as it conducted one of those operations in the South China Sea.

“In the South China Sea, China’s actions in particular are causing anxiety and raising regional tensions,” Carter told sailors aboard the ship. “In response, countries across the Asia-Pacific, both long-standing allies and new partners, are reaching out anew to the United States, to uphold the rules and principles that have allowed the region to thrive. And we’re answering that call.”

Carter also mentioned the possible use of U.S. underwater drones in the South China Sea.

The Pentagon is investing in “new undersea drones in multiple sizes and diverse payloads that can, importantly, operate in shallow water, where manned submarines cannot”, said Carter.

“The idea is that if we were ever to get into a bust-up in the South China Sea, the Chinese would not know for sure what sort of capabilities the US might have,” said Shawn Brimley, a former White House and Pentagon official now at the Center for a New American Security. “This might have some deterrent impact on the potential for provocative behavior.”