US details alleged Chinese nuclear test, urges disarmament

A U.S. State Department official disclosed declassified details Monday of what the U.S. says was a Chinese underground nuclear test six years ago, presenting seismic data collected from an international monitoring station to support the allegation. The disclosure, made in Geneva before a U.N.-backed arms-control body, came as the last nuclear-limits agreement between Washington and Moscow expired, ending restrictions on the world’s two largest nuclear arsenals and raising concerns about a potential new arms race.

The U.S. assertion underscores deepening tensions over nuclear weapons policy as the Trump administration signals willingness to resume testing and presses China and Russia to engage in new disarmament talks.

The Alleged Test

Christopher Yeaw, the State Department’s assistant secretary for arms control and nonproliferation, told the U.N.-backed Conference on Disarmament that seismic monitoring equipment detected an explosion at the Lop Nur underground test site in western China on June 22, 2020. The recorded seismic event measured magnitude 2.75 at a monitoring station in neighboring Kazakhstan.

Yeaw said the seismic signals matched the characteristics of a nuclear explosion rather than routine mining activity. “The seismic signals were indicative of a single fire explosion, not typical of mining explosions,” he said, noting the assessment was based on comparisons with historical explosions and earthquakes.

The U.S. official said China has made it difficult for the international community to verify whether further tests have occurred, and that Beijing rejected allowing seismic monitoring stations to be positioned at distances to Lop Nur comparable to those the U.S. permits near its test site in Nevada.

China’s Response

China’s ambassador to the Conference on Disarmament, Jian Shen, rejected the allegations categorically. “Beijing resolutely rejects the unfounded accusations by the U.S. and has dismissed the continued distortion and criticism of China’s nuclear policy,” he said.

Shen characterized the U.S. assertion as a pretext. “The U.S. accusation that China conducted a nuclear explosion test is completely unfounded and is merely a pretext for resuming its own nuclear testing,” he said.

The Chinese ambassador also argued that his country’s arsenal remains smaller than those of the United States or Russia, and that Beijing has “always adhered” to commitments suspending nuclear testing. He said China has “never” engaged in activities violating the Comprehensive Nuclear Test Ban Treaty.

Arsenal Growth and Expiring Limits

Secretary of State Marco Rubio provided numerical details on China’s nuclear expansion. “Since 2020, China has increased its nuclear weapons stockpile from the low 200s to more than 600 and is on pace to have more than 1,000 warheads by 2030,” Rubio wrote.

Yeaw said the U.S. intelligence assessment projected even faster growth. “We believe China may achieve parity within the next four or five years,” he told the conference, referring to nuclear weapons capability comparable to that of the United States.

The disclosure came weeks after the New START treaty, the last bilateral nuclear-arms-control agreement between Washington and Moscow, expired this month. The treaty had limited each country to 1,550 deployed strategic warheads. Its expiration ended the only remaining numerical constraints on the nuclear arsenals of the world’s two largest weapons powers.

Yeaw cited New START’s shortcomings in his remarks. The treaty, he said, had failed to address Russia’s large arsenal of nonstrategic nuclear weapons, which totals up to 2,000 warheads. He told the conference that the agreement’s “greatest flaw was that New START did not account for the unprecedented, deliberate, rapid and opaque nuclear weapons buildup by China.”

U.S. Testing Plans and Diplomacy

The U.S. statements on disarmament come against the backdrop of Trump administration signals about potentially resuming nuclear weapons testing. In October, President Donald Trump indicated the U.S. would return to testing for the first time since 1992, though Energy Secretary Chris Wright later clarified that any such tests would not include nuclear explosions.

At the Hudson Institute in Washington last week, Yeaw said the U.S. position on testing would respond to the standards set by other nuclear powers. He referenced Trump’s previous comments by saying the U.S. would pursue testing on an “equal basis,” which he said does not mean atmospheric testing but rather assumes a reciprocal response to whatever standard China or Russia establishes.

In his first term, Trump attempted to negotiate a three-way nuclear agreement involving China, an effort that ultimately failed. Secretary of State Rubio signaled Washington’s commitment to pursuing multiple diplomatic channels. “Pursuing all avenues to fulfill Trump’s desire for a world with fewer of these awful weapons,” Rubio said, while insisting the U.S. would not “stand by while Russia and China expand their nuclear forces.”

Yeaw told the Conference on Disarmament that the U.S. looked to all participating nations to encourage China and Russia to engage meaningfully in multilateral disarmament discussions. The conference brings together some 65 countries to address issues including nuclear, biological, and chemical weapons.