By Michael R. Gordon

The U.S. presented new seismic data Tuesday to buttress its recent allegation that China has secretly carried out low-yield nuclear tests, challenging Beijing's insistence that it has scrupulously observed an international accord banning all nuclear detonations.

A senior State Department official said that a seismic monitoring station in Kazakhstan had detected a 2.75 magnitude event on June 22, 2020. The U.S. has accused China of conducting a clandestine low-yield nuclear test at that time.

"We are aware that China conducted a nuclear explosive test," said Christopher Yeaw, an assistant secretary of state. He said the probable explosion occurred near Lop Nor in northwest China, which has long served as China's main nuclear test site.

The U.S. allegation comes at a time when the Trump administration is seeking to pressure Beijing to join potential talks with the U.S. and Russia on drafting a new accord to limit nuclear weapons. The question of how to limit nuclear arms is all the more pressing as it follows the expiration earlier this month of the New Start treaty that reduced U.S. and Russian long-range nuclear arms.

President Trump is planning to visit Beijing for a summit with Chinese leader Xi Jinping in April.

Trump said last year that the U.S. would resume nuclear testing "on an equal basis" with China and Russia. The administration has yet to order a resumption of nuclear tests, but American officials have said that if they proceed, any U.S. tests would be similar to the low-yield nuclear detonations it has accused China and Russia of conducting.

China has repeatedly denied allegations that it has carried out such tests. China's embassy in Washington didn't immediately respond to a request for comment about the seismic data cited by Yeaw.

The Comprehensive Nuclear Test Ban Treaty of 1996 allows signatories to carry out activities to assure the safety and reliability of their nuclear arsenal, including experiments involving fissile material, as long as they don't result in a nuclear-explosive yield.

The question is whether China has crossed that line, as the Trump administration now alleges, and whether the U.S. needs to respond in kind or can continue to rely on supercomputers and other techniques to maintain and upgrade its nuclear arsenal.

The treaty isn't legally in force because not enough nations have ratified it, but major powers including China, Russia and the U.S. say they are abiding by its terms.

The organization that was established to monitor the treaty said earlier this month that its monitoring system had not detected any evidence of a Chinese nuclear explosion on June 22, 2020.

But Robert Floyd, the executive secretary of the organization, revised that assessment Tuesday, noting in a statement that "two very small seismic events," 12 seconds apart, had been detected on that date.

Floyd said the organization is capable of detecting underground explosions that might be nuclear tests if they have a yield equivalent to about 500 tons of TNT. Because the suspected blasts were so small, Floyd added, "it is not possible to assess the cause of these events with confidence" using seismic data alone.

The bomb that the U.S. dropped on Hiroshima in 1945 produced an explosive equivalent to about 15,000 tons, or 15 kilotons.

Yeaw, who made his comments in an appearance at the Hudson Institute in Washington, said that the U.S. didn't know the nuclear yield of the alleged June 2020 test because of China's efforts to mask the seismic signature.

But he said such low-yield tests would help Beijing to update and expand its nuclear forces. The seismic signals that had been detected that day weren't consistent with an earthquake or mining explosions, he said.

The U.S. has long had concerns about clandestine low-level tests. The Journal reported in April 2020 that the U.S. was concerned that China might be secretly conducting nuclear tests at its Lop Nor site. The U.S. said in 2019 that Russia was also likely conducting low-yield nuclear tests.

Some arms-control proponents say the U.S. should seek to resolve its concerns over possible Chinese and Russian violations by starting technical talks with those countries on ways to detect and deter very low-yield nuclear tests.

"Any U.S. resumption of testing in response to such allegations would be technically unnecessary and would set off a chain reaction of nuclear testing by other nuclear-armed states," said Daryl Kimball, the executive director of the Arms Control Association.

Yeaw said the U.S., China and Russia "could creatively think about" new verification approaches. But allowing China and Russia to conduct low-yield tests while the U.S. refrained from such activities, he said, would leave Washington at an "intolerable disadvantage."

He said expected to discuss nuclear issues with Chinese and Russian officials at a United Nations forum in Geneva next week.

Write to Michael R. Gordon at michael.gordon@wsj.com

(END) Dow Jones Newswires

February 17, 2026 17:26 ET (22:26 GMT)

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