China almost certainly shook neighbouring Kazakhstan with an underground nuclear weapons test, according to a senior American official.

Seismic activity detected in Kazakhstan on June 22, 2020 appeared to stem from such a test rather than a natural earthquake, Reuters on February 18 reported Christopher Yeaw, US assistant secretary of state, as telling an event at the Hudson Institute in Washington.

Yeaw was cited as saying that he had “virtually no doubt” that a magnitude-2.75 tremor registered in Kazakhstan — roughly 750 kilometres (466 miles) from China’s Lop Nur testing ground — stemmed from an underground detonation, the news agency’s report said.

“This [seismic activity] is completely inconsistent with an earthquake. It is what you would expect from a nuclear test,” Yeaw, a former intelligence analyst who holds a doctorate in nuclear engineering, was further quoted as stating.

He reportedly added that Beijing sought to mask the blast by detonating the device within a large subterranean cavity, a technique designed to dampen seismic shockwaves and make detection more difficult.

The Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO), which if fully established would monitor compliance with a global ban on creating nuclear explosions – should that ban enter into force following sought ratifications from several countries yet to back the prohibition – said it lacked sufficient evidence to substantiate Yeaw’s assertions.

The Chinese embassy in Washington dismissed the allegations from Yeaw as “completely groundless”, accusing the US of attempting to “fabricate pretexts” to justify resuming its own nuclear testing.

“This is political manipulation aimed at achieving nuclear hegemony and evading its own nuclear disarmament obligations,” Reuters quoted Chinese embassy spokesperson Liu Pengyu as saying in an emailed statement. “China strongly urges the United States to reaffirm its commitment to refraining from nuclear testing, support the global consensus against nuclear tests, and take concrete steps to safeguard the international nuclear disarmament and non-proliferation regime.”

The row comes as US President Donald Trump presses Beijing to join Washington and Moscow in negotiations to replace New START, the bilateral treaty limiting US and Russian strategic nuclear arsenals that expired on February 5. The lapse of the agreement has fuelled concerns that the world could be entering a renewed phase of competition in nuclear weapons.