The New START treaty terminated Thursday, leaving no caps on the two largest atomic arsenals for the first time in more than a half-century and fueling fears of an unconstrained nuclear arms race.

Russian President Vladimir Putin had declared his readiness to stick to the treaty’s limits for another year if Washington followed suit. But U.S. President Donald Trump has argued that he wants China to be a part of a new treaty, and his administration ramped up the pressure by accusing Beijing of carrying out nuclear explosive tests. Beijing rejected the allegations and has rebuffed efforts to have it join a nonproliferation deal.

U.S. Secretary of State Marco Rubio reiterated that China should be involved in a potential new nuclear treaty. “An arms control arrangement that does not account for China’s build-up, which Russia is supporting, will undoubtedly leave the United States and our allies less safe,” he said.

Russian and U.S. negotiators discussed the future of nuclear arms control in the United Arab Emirates, where Russian, Ukrainian and U.S. delegations held two days of talks on a peace settlement in Ukraine, Kremlin spokesman Dmitry Peskov told reporters Friday.

“There is an understanding, and they talked about it in Abu Dhabi, that both parties will take responsible positions and both parties realize the need to start talks on the issue as soon as possible,” Peskov said.

Asked to comment on a report by Axios claiming Russian and U.S. negotiators discussed a possible informal deal to observe the pact’s limits for at least six months, Peskov responded that any such extension could only be formal.

“It’s hard to imagine any informal extension in this sphere,” Peskov said.

The U.S. wants a new deal involving China

Trump has indicated he would like to keep limits on nuclear weapons but wants to involve China in a potential new treaty.

In his first term, Trump tried and failed to push for a three-way nuclear pact involving China. Beijing has balked at any restrictions on its smaller but growing nuclear arsenal, while urging the U.S. to resume nuclear talks with Russia.

Rubio said the U.S. was “pursuing all avenues” to fulfill Trump’s “desire for a world with fewer of these awful weapons,” but insisted Washington would not stand still while Russia and China expand their nuclear forces.

“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 on Substack.

Thomas DiNanno, a top U.S. diplomat in charge of arms control, said Friday that the expiration of the last Russia-U.S. nuclear arms pact marks the “end of an era” of what he described as “U.S. unilateral restraint.” He said Trump wants a “better agreement” that would also involve Beijing.

“As we sit here today, China’s entire nuclear arsenal has no limits, no transparency, no declarations and no controls,” DiNanno told the Conference on Disarmament, a U.N.-backed organization, in Geneva.

DiNanno also accused Beijing of covertly conducting nuclear tests. “Today, I can reveal that the U.S. government is aware that China has conducted nuclear explosive tests, including preparing for tests with designated yields in the hundreds of tons,” he said.

DiNanno stated that China’s army “sought to conceal testing by obfuscating the nuclear explosions because it recognizes these tests violate test ban commitments.”

The comment follows earlier U.S. statements accusing Beijing of covertly conducting nuclear tests.

Ambassador Shen Jian of China rejected what he called “false narratives and unfounded accusations by the United States,” saying that “we abide by our commitment to suspend nuclear testing.”

“The U.S.’s continuous hyping up of China’s nuclear arsenal expansion is essentially aimed at shifting its own responsibility for nuclear disarmament and seeking excuses for promoting nuclear hegemony,” Shen said.

He said that “at this stage, China will not participate in nuclear disarmament negotiations” because its nuclear capabilities ”are not on the same scale as those of the United States or Russia.”

Shen said Beijing regrets the New START’s expiration and urged the U.S. to accept Moscow’s offer to stick to the treaty’s limits and quickly resume nuclear talks with Russia.

New START provisions

New START, signed in 2010 by then-President Barack Obama and his Russian counterpart, Dmitry Medvedev, was the last remaining pact in a long series of agreements between Moscow and Washington to limit their nuclear arsenals, starting with SALT I in 1972.

New START 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 set to expire in 2021 but was extended for five years.

The pact envisioned sweeping on-site inspections to verify compliance, although they stopped in 2020 because of the COVID-19 pandemic and never resumed.

In February 2023, Putin suspended Moscow’s participation, saying Russia couldn’t allow U.S. inspections of its nuclear sites at a time when Washington and its NATO allies openly declared they wanted Moscow’s defeat in Ukraine. At the same time, the Kremlin emphasized it wasn’t withdrawing from the pact altogether, pledging to respect its caps on nuclear weapons.

In September, Putin offered to keep the New START’s limits for another year to buy time for both sides to negotiate a successor agreement.

Even as New START expired, the U.S. and Russia agreed Thursday to reestablish high-level, military-to-military dialogue following a meeting between senior officials from both sides in Abu Dhabi, the U.S. 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.

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Keaten reported from Geneva. Ken Moritsugu in Beijing contributed to this report.