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WASHINGTON has renewed accusations that China conducted a covert underground nuclear test in 2020, citing seismic data it says point to a contained explosion at the Lop Nor site, a charge Beijing has firmly denied.
Reuters cited on Wednesday that a senior United States official has disclosed what he described as new evidence suggesting that China carried out a low-yield underground nuclear test in June 2020, intensifying already strained nuclear diplomacy between the two powers.
Christopher Yeaw, the U.S. Assistant Secretary of State, told an event at the Hudson Institute in Washington that seismic readings from a remote monitoring station in Kazakhstan detected what he characterised as a contained explosion at China’s Lop Nor nuclear test grounds in western China on June 22, 2020.
The station, located approximately 450 miles from the site, recorded an event with a magnitude of 2.75.
“I’ve looked at additional data since then. There is very little possibility I would say that it is anything but an explosion, a singular explosion,” Yeaw said, adding that the readings were not consistent with mining activity.
Seismic readings from a remote monitoring station in Kazakhstan detected what he characterised as a contained explosion at China’s Lop Nor nuclear test grounds in western China,” he added. “It is ... what you would expect with a nuclear explosive test.”
Yeaw, a former intelligence analyst and defence official with a doctorate in nuclear engineering, suggested that the device may have been detonated using a technique known as decoupling, in which an explosive is set off within a large underground cavity to dampen seismic shockwaves and mask the scale of the blast.
However, the Comprehensive Nuclear-Test-Ban Treaty Organization, which operates a global monitoring system designed to detect nuclear explosions, said the available data were insufficient to substantiate the allegation.
The organisation’s executive secretary, Robert Floyd, stated that the PS23 seismic station in Kazakhstan recorded “two very small seismic events” twelve seconds apart on the date in question.
“These two events were far below that level. As a result, with this data alone, it is not possible to assess the cause of these events with confidence,” Floyd said, noting that the system is calibrated to detect events consistent with nuclear explosions equivalent to 500 metric tonnes of TNT or greater.
China categorically rejected the U.S. claim. Liu Pengyu, spokesperson for the Chinese embassy in Washington, described the accusation as “entirely unfounded” and accused the United States of seeking “to fabricate excuses for resuming” its own nuclear testing.
“This is political manipulation aimed at pursuing nuclear hegemony and evading its own nuclear disarmament responsibilities,” Liu said in a statement.
“China urges the U.S. to reaffirm the five nuclear-weapon states' commitment on refraining from nuclear tests, uphold the global consensus against nuclear tests, and take concrete steps to safeguard the international nuclear disarmament and non-proliferation regime,” he added.
The dispute unfolds as President Donald Trump presses China to join the United States and Russia in negotiating a successor agreement to New START, the last remaining U.S.-Russia strategic nuclear arms limitation treaty, which expired on February 5.
The lapse of that accord has heightened concerns that the world may be entering a renewed phase of nuclear arms competition.
China signed but has not ratified the 1996 Comprehensive Nuclear-Test-Ban Treaty and maintains that it has complied with its obligations.
Beijing has previously rejected calls for a trilateral arms control pact, arguing that its nuclear arsenal remains far smaller than those of Washington and Moscow.
According to the Pentagon, China currently possesses more than 600 operational nuclear warheads and is expanding its strategic forces, with projections suggesting it could field more than 1,000 warheads by 2030.
The United States last conducted an underground nuclear test in 1992 and now relies on advanced simulations and laboratory research to maintain its arsenal. - February 18, 2026