(Bloomberg) -- The US Department of Energy said it’s willing to prove its engineers aren’t breaking a three-decade moratorium against testing nuclear weapons, in a bid to encourage China and Russia to be more transparent and defuse military tensions.

The offer to allow international observers to witness sensitive US weapons-related tests, floated on the sidelines of an International Atomic Energy Agency meeting in Vienna this week, comes at a critical moment for arms control. Earlier this year, Vladimir Putin withdrew Russia from its last agreement with the US that limited nuclear arsenals and Pentagon officials are increasingly on edge about China’s expanding stockpile of fissile material. 

“We are committed to our nuclear-testing moratorium,” said Corey Hinderstein, a senior nonproliferation official at the National Nuclear Security Administration, which oversees the US stockpile of more than 5,000 warheads. “We have no problem with proving it.” 

“We’ve even offered mutual and reciprocal actions” to Russia and China, she said. “We’ve not gotten a response.”

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Analysts warned this month that satellite images of atomic-test sites in China, Russia and the US all showed signs of increased activity. Nuclear saber-rattling has increased in the wake of Russia’s invasion of Ukraine, with Putin ordering his forces ready to resume testing on short notice in February. 

“Mutual suspicions are being used by advocates in all three countries who would wish to resume the explosive testing of nuclear weapons,” wrote Jeffrey Lewis, a researcher at the Middlebury Institute of International Studies. “If one country explodes a nuclear weapon, the other two are likely to follow suit.”

China, Russia and the US all continue to abide by an international legal norm established under the Comprehensive Test Ban Treaty, whose organization runs a global network of sensors designed to detect a nuclear detonation. 

But more transparency is needed because while the countries don’t test warheads, they do conduct so-called sub-critical experiments — explosions that verify weapon designs without the volume of atomic material needed to sustain a chain reaction. Those smaller explosions can still be picked up by sensitive seismic stations and raise suspicion between rivals. 

“We recognize some of the questions that have been raised,” said Hinderstein, adding that the US is preparing two sub-critical tests in 2024. “Even though we feel we are being more transparent than anyone else in the world, we’re looking to go even further.” 

While the Department of Energy has considered inviting international observers for months, it’s still not clear what form that would take. Monitors would be invited to the Nevada National Security Site, where the tests are slated to take place. They may be allowed to take radiation measurements and review data, ensuring that experiments conducted within permissible limits. While the US would like to see China and Russia reciprocate, their refusal wouldn’t necessarily be a deal-breaker, according to Hinderstein. 

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