US President Donald Trump on Thursday rejected an offer from his Russian counterpart to voluntarily extend the caps on strategic nuclear weapons deployments after the treaty that held them in check for more than two decades expired.
"Rather than extend 'New START'...we should have our nuclear experts work on a new, improved and modernised treaty that can last long into the future," Trump wrote in a post on social media.
Trump was responding to a proposal by Russian President Vladimir Putin for the sides to adhere for a year to the limits set by the 2010 accord on deployments of strategic nuclear warheads and the missiles, aircraft and submarines that carry them. New START was the last arms control treaty between the world's two largest nuclear weapons powers.
It allowed for only a single extension, which Putin and former US President Joe Biden agreed to for five years in 2021. Earlier, Kremlin spokesman Dmitry Peskov said Russia was still ready to engage in dialogue with the US if Washington responded constructively to Putin's proposal.
"Listen, if there are any constructive replies, of course we will conduct a dialogue," Peskov told reporters. New START was the last in a series of nuclear agreements between Moscow and Washington dating back more than half a century to the Cold War.
Besides setting numerical limits on weapons, they included inspection regimes experts say served to build a level of trust and confidence between the nuclear adversaries, helping make the world safer. If nothing replaces the treaty, security analysts see a more dangerous environment with a higher risk of miscalculation.
Forced to rely on worst-case assumptions about the other's intentions, the US and Russia would see an incentive to increase their arsenals, especially as China plays catch-up with its own rapid nuclear build-up.
UN Secretary-General Antonio Guterres said on Wednesday that the dissolution of decades of achievement in arms control, "could not come at a worse time – the risk of a nuclear weapon being used is the highest in decades."
He urged the sides to resume negotiations without delay to agree a successor framework restoring verifiable limits. Asked about the report of talks, UN spokesperson Stephane Dujarric told a regular briefing at the United Nations in New York: "This is a very dangerous period not to have a framework dealing with these nuclear weapons."
"We hope very much that the talks will be positive and will be fruitful." Trump has said he wants to replace New START with a better deal, bringing in China.
But Beijing has declined negotiations with Moscow and Washington. It has a fraction of their warhead numbers - an estimated 600, compared to around 4,000 each for Russia and the US.
Repeating that position on Thursday, China said the expiration of the treaty was regrettable, and urged the US to resume dialogue with Russia on "strategic stability." Peskov said Russia would take a responsible approach.
The White House said this week that Trump would decide the way forward on nuclear arms control, which he would, "clarify on his own timeline." There was confusion over the exact timing of the expiry, but Peskov said it would be at the end of Thursday.
Former Russian President Dmitry Medvedev, who signed the treaty with then US President Barack Obama in 2010, said on Wednesday that New START and its predecessors were now "all in the past." Russia's Foreign Ministry said Moscow's assumption was that the treaty no longer applied and both sides were free to choose their next steps.
It said Russia was prepared to take "decisive military-technical countermeasures to mitigate potential additional threats to national security" but was also open to diplomacy.
Ukraine, which has been at war with Russia since Moscow's 2022 invasion, said the treaty's expiry was a consequence of Russian efforts to achieve the "fragmentation of the global security architecture" and called it, "another tool for nuclear blackmail to undermine international support for Ukraine."
Strategic nuclear weapons are the long-range systems that each side would use to strike the other's capital, military and industrial centres in the event of a nuclear war. They differ from so-called tactical nuclear weapons that have a lower yield and are designed for limited strikes or battlefield use.
If left unconstrained by any agreement, Russia and the US could each, within a couple of years, deploy hundreds more warheads beyond the New START limit of 1,550, experts say.
"Transparency and predictability are among the more intangible benefits of arms control and underpin deterrence and strategic stability," said Karim Haggag, director of the Stockholm International Peace Research Institute.
(Reporting by Dmitry Antonov in Moscow and Mark Trevelyan in London; additional reporting by Mei Mei Chu in Beijing, Shubham Kalia in Bengaluru, Andrea Shalal, Jonathan Landay and David Brunnstrom in Washington. Editing by Timothy Heritage and Mark Porter)