A new State Department report on compliance with arms control, nonproliferation and disarmament, first obtained by the Wall Street Journal earlier Wednesday, found that China may be flouting international law by conducting the tests within the northwest region of the country, using low explosive power.
The report didn't prove any wrongdoing on the part of the Chinese, but still raised red flags.
"Some compliance concerns are raised and some findings of violations are made," it read.
Officials wrote that China had maintained a "high level of activity" at its Lop Nur site in 2019, and could be seeking to operate it year-round going forward.
It also mentioned China’s use of explosive containment chambers, extensive evacuations at the site and lack of transparency on nuclear testing as reasons for raising suspicions.
The report went on to cite further concerns about China's possible violation of the Biological Weapons Convention (BWC) by engaging "in biological activities with potential dual-use application."
The U.S. government also could not determine if China had shut down its biological warfare program, nor could it confirm if Beijing still had access to such weapons, due to its lack of openness and transparency.
China has been under growing scrutiny over its handling of the novel coronavirus (COVID-19) outbreak. There is increasing confidence that COVID-19 likely originated in a Wuhan laboratory not as a bioweapon, but as part of China's effort to demonstrate that its efforts to identify and combat viruses were equal to or greater than the capabilities of the United States, multiple sources who have been briefed on government actions and seen relevant materials revealed to Fox News.
Secretary of State Mike Pompeo called out the Chinese government for not sharing the full story with the rest of the world.
"We know that this virus originated in Wuhan, China," Pompeo told "The Story". "We know there is the Wuhan Institute of Virology just a handful of miles away from where the wet market was. There is still lots to learn. The United States government is working diligently to figure it out."
Fox News' Bret Baier, Gregg Re, Charles Creitz and Martha MacCallum contributed to this report.