The last remaining arms control treaty limiting the United States and Russia’s most powerful nuclear weapons expired overnight, with no clear signal from either government that negotiations on a replacement are imminent.

President Donald Trump, who suggested last fall he might support renewing the New START agreement, reversed course last month, saying he was comfortable letting it lapse and favoring a broader deal that would include additional countries.

In a social media post Thursday, Trump said that instead of extending New START — which he accused Russia of violating — the United States should direct its nuclear experts to pursue “a new, improved, and modernized Treaty that can last long into the future.”

Secretary of State Marco Rubio echoed that position Wednesday, arguing that any future arms control agreement must include China, despite Beijing’s nuclear arsenal being far smaller than those of the U.S. and Russia.

“The president has been clear that meaningful arms control in the 21st century cannot exclude China, given its rapidly expanding nuclear capabilities,” Rubio said.

Kremlin spokesman Dmitry Peskov confirmed the treaty’s expiration on Thursday, calling it a regrettable development. He said Russian President Vladimir Putin had previously offered to extend the agreement, but received no response from Washington.

China swiftly rejected the idea of joining a trilateral framework. Foreign Ministry spokesperson Lin Jian said Beijing’s nuclear forces are not comparable to those of the U.S. and Russia, making such talks “neither fair nor reasonable” at this stage.

New START, which capped deployed strategic nuclear warheads and delivery systems, had been the cornerstone of U.S.-Russia arms control for more than a decade. Its expiration leaves the world’s two largest nuclear powers without any binding limits on their arsenals for the first time in decades.