The last remaining nuclear arms pact between Russia and the United States has expired, removing any caps on the two largest atomic arsenals for the first time in more than half a century.
The termination of the New START Treaty could set the stage for what many fear could be an unconstrained nuclear arms race, with UN Secretary General António Guterres calling it a "grave moment for international peace and security".
On Thursday, the Kremlin said it regretted the pact's expiration, while US President Donald Trump declared he opposed maintaining its limits and wants a better deal.
Russian President Vladimir Putin last year declared his readiness to stick to the treaty's limits for another year if Washington followed suit, but Mr Trump has ignored the offer and argued that he wants China to be a part of a new pact — something Beijing has rebuffed.
"Rather than extend 'NEW START' (A badly negotiated deal by the United States that, aside from everything else, is being grossly violated), we should have our Nuclear Experts work on a new, improved, and modernised Treaty that can last long into the future," Mr Trump posted on his Truth Social network.
Mr Putin discussed the pact's expiration with Chinese leader Xi Jinping on Wednesday, noting the US failure to respond to his proposal to extend its limits.
Kremlin spokesperson Dmitry Peskov said Moscow viewed the treaty's expiration on Thursday "negatively" and regretted it.
Russia will "act in a balanced and responsible manner based on thorough analysis of the security situation," Kremlin adviser Yuri Ushakov added.
He said Russia would maintain its "responsible, thorough approach to stability when it came to nuclear weapons," adding that "of course, it will be guided primarily by its national interests."
With the end of the treaty, Moscow "remains ready to take decisive military-technical measures to counter potential additional threats to the national security," the Russian Foreign Ministry said.
Mr Guterres said 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 said.
He urged the parties to resume negotiations without delay to agree on a successor framework that restores verifiable limits.
Arms control advocates also bemoaned the end of New START and warned of the imminent threat of a new arms race.
"If the Trump administration continues to stiff-arm nuclear arms control diplomacy with Russia and increase the number of nuclear weapons ... it will only lead Russia to follow suit and encourage China to accelerate its ongoing strategic build-up in an attempt to maintain a strategic nuclear retaliatory strike capability vis-a-vis the United States," said Daryl Kimball, executive director of the Arms Control Association in Washington.
"Such a scenario could lead to a years-long, dangerous three-way nuclear arms build-up."
Even as New START expires, the US and Russia agreed to re-establish high-level military-to-military dialogue following a meeting of senior officials in Abu Dhabi, the US military command in Europe said.
The link was suspended in 2021 as relations between Moscow and Washington grew increasingly strained before Russia sent troops into Ukraine in February 2022.
Meanwhile, Ukraine and Russia concluded a second round of US-brokered talks in Abu Dhabi on Thursday aimed at ending the war, with the two sides conducting a prisoner swap and agreeing to resume negotiations soon.
What is the New START treaty pact?
New START was the last remaining treaty in a long series of agreements between Moscow and Washington to limit their nuclear arsenals, beginning with SALT I in 1972.
Signed in 2010 by then-president Barack Obama and his Russian counterpart, Dmitry Medvedev, the pact restricted each side to no more than 1,550 nuclear warheads on no more than 700 missiles and bombers — deployed and ready for use.
It was originally scheduled to expire in 2021, but was extended by five years.
The pact envisioned sweeping on-site inspections to verify compliance, but they were suspended in 2020 due to the COVID-19 pandemic and never resumed.
In February 2023, Mr Putin suspended Moscow's participation, saying Russia couldn't allow US inspections of its nuclear sites at a time when Washington and its NATO allies have openly declared Moscow's defeat in Ukraine as their goal.
At the same time, the Kremlin emphasised it wasn't withdrawing from the pact altogether, pledging to respect its caps on nuclear weapons.
In offering in September to abide by New START's limits for a year to buy time for both sides to negotiate a successor agreement, Putin said the treaty's expiration would be destabilising and could fuel nuclear proliferation.
Trump wants China in new pact
Mr Trump has indicated he would like to keep limits on nuclear weapons —but wants to involve China in a potential new treaty.
US Secretary of State Marco Rubio said that Mr Trump had made clear "in order to have true arms control in the 21st century, it's impossible to do something that doesn't include China because of their vast and rapidly growing stockpile".
In his first term, Mr Trump tried and failed to push for a three-way nuclear pact involving China.
Beijing has baulked at any restrictions on its smaller but growing nuclear arsenal, while urging the US to resume nuclear talks with Russia.
"China's nuclear forces are not at all on the same scale as those of the US and Russia, and thus China will not participate in nuclear disarmament negotiations at the current stage," Foreign Ministry spokesperson Lin Jian said.
He said China regretted the expiration of New START and called on the US to resume nuclear dialogue with Russia soon and to continue observing the treaty's core limits for now.
Mr Peskov reaffirmed on Thursday that Moscow respected Beijing's position.
He and other Russian officials have repeatedly argued that any attempt to negotiate a broader nuclear pact instead of a US-Russian deal should also involve nuclear arsenals of NATO members France and the UK.
AP/Reuters
