The United States military is considering sending aircraft and Navy ships to enforce freedom of navigation around a chain of rapidly expanding Chinese-made artificial islands in the disputed waters of the South China Sea, U.S. officials said Tuesday. The move comes amid growing concerns among Pentagon officials that Beijing is strengthening its efforts to expand its influence in the strategic waterway critical to world trade.

According to the officials, U.S. Defense Secretary Ash Carter has proposed to deploy Navy surveillance aircraft and U.S. naval ships within 12 nautical miles of reefs that China has been constructing in the Spratly Islands. If approved by the U.S. government, such a move would directly challenge Beijing’s territorial claims in the region in what the U.S. considers to be international waters and airspace, the Wall Street Journal reported.

“We are considering how to demonstrate freedom of navigation in an area that is critical to world trade,” Reuters quoted a U.S. official as saying, adding that any final decision would need the White House's approval.

The U.S., which said that the man-made islands cannot be recognized as sovereign Chinese territory, may be expecting that any possible deployments of military units in the region would impact the Chinese aggression. However, the move could also backfire if China decides to double down its efforts in defiance of the U.S., the Journal reported.

“The risk of this is that China may use such deployments as a reason to try to challenge or confront U.S. forces,” Rory Medcalf, head of the National Security College at the Australian National University, told Reuters.

Meanwhile, Chinese embassy spokesman Zhu Haiquan told Reuters that China had “indisputable sovereignty” over the Spratly Islands, and that the country’s construction in the area was “reasonable, justified and lawful.”

China has expanded the artificial islands in the Spratly Islands to 2,000 acres of land, which is significantly up from 500 acres last year, according to a February estimate by experts who studied the images released by IHS Jane’s, a defense intelligence provider. 

Last month, IHS Jane's Defence Weekly released more satellite images showing that China was building an airstrip on the northeastern side of Fiery Cross Reef, part of the Spratly Islands chain claimed by at least three other countries, including the Philippines and Vietnam.

The Philippines, which was recently accused by China of breaching an informal code of conduct between regional nations in the South China Sea, said that urgent action must be taken to stop China’s expansion.

“We are taking the position that we must do something quickly lest the massive reclamation results in the de facto control by China of the South China Sea,” Reuters quoted Albert Ferreros del Rosario, the secretary of foreign affairs of the Philippines, as saying at the Center for Strategic and International Studies think tank in Washington.