According to a secret US military assessment, the Chinese military may soon deploy a high-altitude espionage drone that flies at least three times the speed of sound, according to the Washington Post late Tuesday.

The publication referenced a National Geospatial-Intelligence Agency confidential document.

According to the publication, the document, which Reuters could not independently authenticate or verify, includes satellite images dated August 9 that shows two WZ-8 rocket-propelled reconnaissance drones at an air base in eastern China, approximately 350 miles (560 kilometers) inland from Shanghai.

The U.S. assessment said China’s People’s Liberation Army (PLA) had “almost certainly” established its first unmanned aerial vehicle unit at the base, which falls under the Eastern Theater Command, the branch of the Chinese military responsible for enforcing Chinese sovereignty claims over Taiwan, the newspaper reported.

The U.S. Defense Department did not immediately respond to a request for comment. The Chinese government could not immediately be reached for comment.

The Washington Post said it obtained the assessment of the program from a trove of images of classified files posted on the Discord messaging app, allegedly by a member of the Massachusetts Air National Guard, who was arrested last week.

The FBI on Thursday arrested Jack Douglas Teixeira, a 21-year-old member of the U.S. Air National Guard, over the leaks online of classified documents that embarrassed Washington with allies around the world.

The leaks first became widely known earlier this month, setting Washington on edge about the damage they may have caused. The episode embarrassed the U.S. by revealing its spying on allies and purported Ukrainian military vulnerabilities.

Taiwan president Tsai Ing-wen’s recent meeting with U.S. House of Representative Kevin McCarthy had upset Beijing. China, which claims democratically ruled Taiwan is one of its provinces, says Taiwan is the single most important and sensitive issue in its relations with the United States. Taiwan’s government rejects Beijing’s sovereignty claims.