The Trump administration on Tuesday disclosed new intelligence to support its allegation that China conducted a clandestine underground nuclear explosion in 2020 — and confirmed that the United States intends to resume nuclear testing to match what it describes as illicit activity by Beijing and Moscow.

Christopher Yeaw, the assistant secretary of state for arms control and nonproliferation, told an audience at the Hudson Institute in Washington that a remote seismic station in Kazakhstan registered a 2.75-magnitude event on June 22, 2020, originating approximately 450 miles away at Lop Nur, China's primary nuclear test site in the western Xinjiang region.

"There is very little possibility, I would say, that it is anything but an explosion, a singular explosion," Yeaw said. "It is quite consistent with what you would expect from a nuclear explosive test."

The data, he said, was not consistent with an earthquake or mining blasts. Yeaw, a former intelligence analyst and defense official who holds a doctorate in nuclear engineering, said that China had employed "decoupling" techniques — detonating a device inside a large underground cavity — to muffle the blast and confuse international monitoring systems. He described the test as "yield-producing," meaning it triggered a runaway chain reaction in nuclear material, though he declined to specify the size of the explosion.

"We do know that nations don't take these risks without an expectation of significant gain," he said.

International monitors say evidence is inconclusive

The Comprehensive Nuclear-Test-Ban Treaty Organization, whose monitoring station in Kazakhstan recorded the event, offered a more cautious assessment. Executive Secretary Robert Floyd said in a statement Tuesday that the station detected "two very small seismic events, 12 seconds apart" in the time period Yeaw described, but that they fell far below the organization's detection threshold for nuclear explosions — events with yields equivalent to 500 metric tons of TNT or greater.

"With this data alone, it is not possible to assess the cause of these events with confidence," Floyd said.

Independent experts echoed that caution. Ben Dando, head of seismology and verification at NORSAR, a Norwegian organization that monitors for possible nuclear tests, said the ratios of different seismic waves were consistent with an explosion, but the signal was weak and recorded at a single station. "I would not say that there's really strong conclusive evidence," Dando said. "We can't really confirm or deny whether a nuclear test took place at this point."

The Center for Strategic and International Studies, in a recent report, said satellite imagery did not show unusual activity at Lop Nur around the time of the alleged test.

Yeaw pushed back sharply against Floyd's statement, saying the CTBTO chief should "reassess priorities" if his staff cannot detect low-yield tests that nonetheless provide valuable data to nuclear states. "The treaty becomes basically a fig leaf," he said.

China's denial and the broader arms control vacuum

China has forcefully denied the allegations. Liu Pengyu, a spokesperson for the Chinese Embassy in Washington, called the claim "entirely unfounded" and accused the United States of attempting "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. At a press conference last week, Chinese Foreign Ministry spokesperson Lin Jian said the accusations were "completely groundless" and described Washington as "the biggest source of disruption to the international nuclear order."

China's last officially acknowledged nuclear test took place at Lop Nur in 1996. The country has signed but not ratified the Comprehensive Nuclear-Test-Ban Treaty. The United States is in the same position — it signed the treaty under President Bill Clinton, but the Senate rejected ratification in 1999.

The administration's disclosure comes against the backdrop of a widening arms control vacuum. New START, the last binding nuclear arms limitation agreement between the United States and Russia, expired on February 5. President Trump has refused Moscow's offer to extend the treaty for another year, arguing instead for a "new, improved, and modernized" agreement that would include China alongside the United States and Russia.

China has rejected that proposal, contending that its arsenal is far smaller than those of Washington and Moscow and that it should not be bound by the same framework.

The numbers behind the nuclear balance

The gap between the three nuclear powers remains wide, though it is narrowing. China possesses approximately 600 nuclear warheads, according to a Pentagon report released in December. The Defense Department projects that China will field more than 1,000 warheads by 2030. By comparison, Russia holds roughly 4,300 warheads and the United States about 3,700, according to the Stockholm International Peace Research Institute's latest assessment.

But China has relatively little test data to work with. Before the global testing moratorium took hold, China conducted just 45 nuclear tests — about half atmospheric, half underground. The United States, by contrast, has carried out well over a thousand. Some experts have noted that Chinese nuclear scientists would likely gain far more knowledge from each additional test than their American counterparts, given the disparity in historical data.

Satellite imagery has revealed an expansion of equipment areas and housing for personnel at the Lop Nur site in recent years, and at least one new tunnel has been dug. Tong Zhao, a senior fellow at the Carnegie Endowment for International Peace who studies China's nuclear weapons program, said the activity suggests China is "investing significantly into maintaining, if not expanding, the missions at the testing site."

Zhao said he takes the U.S. claims seriously, noting they "may be backed up by some secret U.S. intelligence analysis" and appear consistent with the active status of the Lop Nur facility. Yeaw declined to say whether the United States possesses additional intelligence — including classified data that could detect radioactive signatures or human intelligence — beyond the public seismic readings.

The path to resumed U.S. testing

Yeaw confirmed Tuesday that the United States will follow through on Trump's pledge to resume nuclear testing "on an equal basis" with other nations. But he sought to calibrate expectations about the scale of any future American tests.

"Equal basis doesn't mean we're going back to Ivy Mike-style atmospheric testing in the multi-megaton range," he said, referring to the massive 1952 thermonuclear detonation in the South Pacific. "Equal basis, however, presumes a response to a prior standard. Look no further than China or Russia for that standard."

He did not announce specific timing, saying the president would make that decision, but added that any test would take place at a "level playing field."

"We're not going to remain at an intolerable disadvantage," he said.

The United States last detonated a nuclear device in 1992. Since then, it has relied on a multibillion-dollar program using advanced supercomputer simulations and subcritical experiments — tests that explode small quantities of weapons-grade plutonium without initiating a nuclear chain reaction — to ensure its warheads function properly.

Any resumption of explosive nuclear testing would reverse a post-Cold War norm that has held for more than three decades. Russia's last confirmed nuclear test was conducted in the final days of the Soviet Union in 1990, though the State Department has alleged that Moscow conducted undisclosed tests in recent years. Russia rescinded its ratification of the Comprehensive Nuclear-Test-Ban Treaty in 2023.

Yeaw said he remained hopeful that the United States could enter negotiations with both China and Russia on a new arms control agreement. But he acknowledged that the Pentagon was actively considering whether to expand the American nuclear arsenal by adding warheads to its missiles, bombers, and submarines.

"There are obviously a bunch of options on the table," he said.