China might be secretly conducting nuclear tests with very low explosive power despite Beijing's assertions that it is strictly adhering to an international accord banning all nuclear tests, according to a new arms-control report to be made public by the State Department.
The coming report doesn't present proof that China is violating its promise to uphold the agreement, but it cites an array of activities that "raise concerns" that Beijing might not be upholding the "zero-yield" nuclear-weapons testing ban.
The concerns stem from the high tempo of activity at China's Lop Nur test site, extensive excavations at the site, and China's purported use of special chambers to contain explosions.
Another factor feeding U.S. suspicions is the interruption in past years of data transmissions from monitoring stations on Chinese territory that are designed to detect radioactive emissions and seismic tremors.
The Trump administration's allegation is included in an unclassified summary of an annual review of international compliance with arms-control accords. The review has been in preparation for some time and is likely to add to existing strains over China's handling of the coronavirus pandemic, its militarization of the South China Sea and trade disputes.
It also comes as President Trump is seeking to open nuclear-arms talks with Beijing in the hope of negotiating a new nuclear deal that also includes Russia and covers all nuclear weapons.
Some former arms-control officials said that the Trump administration appeared to be more concerned with scoring points against China than resolving potential disputes through diplomacy.
"If the United States has concerns that nuclear-yield producing testing has been done by China, we should discuss our concerns with Beijing -- and discuss ways to build confidence that such tests are not happening," said Steven Andreasen, who was the top National Security Council official on arms control during the Clinton administration.
China's Embassy in Washington didn't respond to requests for comment.
The agreement at the core of the dispute is the Comprehensive Nuclear Test Ban Treaty, which was concluded in 1996. The accord allows a range of activities to assure the safety and reliability of nuclear weapons, including experiments involving fissile material, as long as they don't produce a nuclear-explosive yield.
The treaty isn't legally in force because not enough nations have ratified it, though major powers, including the U.S. and China, say they are abiding by its terms. While the U.S. and China have signed the agreement, neither has ratified it.
One activity that has fed U.S. suspicions has been interruptions in the flow of data in past years from monitoring stations in China that measure radioactive particles and seismic tremors.
The stations are part of an international network of hundreds of sites set up to verify compliance with the test-ban treaty. Participating nations are responsible for running the stations and have been voluntarily transmitting data to the Vienna-based organization that is to oversee the accord as the agreement has yet to formally go into effect.
A spokeswoman for the body -- the Comprehensive Nuclear Test Ban Treaty Organization -- said there has been virtually no interruption in the data transmissions by the Chinese since September 2019.
Data transmissions were interrupted previously, she said, but that was the result of the negotiating process between the CTBT organization and the Chinese government on arrangements for putting the stations in operation.
"Data transmission from all certified stations was interrupted in 2018 after the testing and evaluation and certification process was completed, " she said. "In August 2019, ongoing negotiations on post-certification activity contracts with Chinese station operators were concluded and data transmission resumed for all five certified stations."
In contrast, the administration's report accuses China of "blocking the flow of data from the monitoring stations."
China likely will double the size of its nuclear stockpile over the next decade, Lt. Gen. Robert Ashley Jr., the director of the U.S. Defense Intelligence Agency, said in a May 2019 appearance at the Hudson Institute, a Washington think tank.
Gen. Ashley noted then that progress China was making "raised questions" whether it was strictly adhering to the test ban treaty. China's arsenal is estimated to be about 300 nuclear warheads, according to the Federation of American Scientists. The U.S. has a stockpile of a 3,800 nuclear warheads that could be carried on long-range and short-range delivery systems, but only 1,700 are deployed, the group says.
Daryl Kimball, the executive director of the Arms Control Association, a nongovernmental group, said activity at Lop Nur isn't proof the Chinese have been engaging in low-yield testing.
"The most effective way to resolve concerns about very low-yield nuclear explosions and enforce compliance with the 1996 Comprehensive Nuclear Test Ban Treaty is for the United States -- and China -- to ratify the treaty and help bring it into force," Mr. Kimball said. "When it does, states have the option to demand intrusive, short-notice on-site inspections."
The U.S. Defense Intelligence Agency asserted last year that Russia had violated the zero-yield standard at its nuclear test site in Novaya Zemlya, a remote archipelago above the Arctic Circle, though it didn't say when this might have occurred.
The new State Department report, which is based on U.S. intelligence, says that the U.S. doesn't know if this occurred in 2019. But it asserts that some Russian's activities since 1996 "have demonstrated a failure to adhere to the U.S. 'zero-yield' standard, which would prohibit supercritical tests."