Satellite images show China has built mock-ups of a U.S. Navy aircraft carrier and destroyer in its northwestern desert, possibly for practice for a future naval clash as tensions rise between the nations.

China has massively upgraded its military in recent years, and its capability and intentions are increasingly concerning to the United States as tensions rise over the South China Sea, Taiwan and military supremacy in the Indo-Pacific.

The images captured by Colorado-based satellite imagery company Maxar Technologies dated Sunday show the outlines of a U.S. aircraft carrier and at least one destroyer sitting on a railway track.

Maxar identified the location as Ruoqiang, a Taklamakan Desert county in the northwestern Xinjiang region.

The independent U.S. Naval Institute said on its website that the mock-ups of U.S. ships were part of a new target range developed by the People’s Liberation Army.

It wasn’t clear from the images how many details had been included in the apparent targets, although USNI said it had identified features on the destroyer including its funnels and weapons systems.

Chinese Foreign Ministry spokesperson Wang Wenbin said at a daily briefing Monday that he had no information about the images, saying, “I’m not aware of the situation you mentioned.”

China’s massive military upgrade has emphasized countering the U.S. and other countries’ naval forces.

That includes the development of land, sea and air-launched missiles to repel and possibly sink opposing vessels, expressed most emphatically by the land-based DF-21D ballistic missile known as the “carrier killer.”

Recent months have also seen a substantial increase in Chinese military flights just southwest of Taiwan, the self-governing island republic claimed by Beijing and which it threatens to annex by force.

Washington provides Taiwan with much of its weaponry and U.S. law requires that it ensures the island can defend itself and treats threats to it as matters of “grave concern.”

The images released by Maxar come amid growing concerns over the possibility of military conflict between the world’s two biggest economies, who are at odds over a litany of political and economic issues.

The Pentagon this month issued a report saying China is expanding its nuclear force much faster than U.S. officials predicted just a year ago. That appears designed to enable Beijing to match or surpass U.S. global power by midcentury, the report said.

U.S. defense officials have said they are increasingly wary of China’s intentions, largely with regard to the status of Taiwan.