MOSCOW (AP) — Another U.S.-Russian nuclear pact is in danger following the U.S. move to withdraw from a Cold War-era arms control treaty, a senior Russian diplomat said Thursday.

Deputy Foreign Minister Sergei Ryabkov charged that the U.S. refusal to negotiate an extension to the New Start treaty signals Washington’s intention to let it expire in 2021. He warned that time is running out to save the pact, which was signed in 2010 by U.S. President Barack Obama and Russian President Dmitry Medvedev.

Ryabkov said that the U.S. has shown “no readiness or desire” to engage in substantive talks on extending the pact, which limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers.

He noted that the U.S. said it has converted 56 Trident submarine-launched intercontinental ballistic missiles and 41 B-52H strategic bombers that carried nuclear weapons for use with conventional weapons, but stonewalled Russia’s repeated requests for a verifiable way to exclude their conversion back to nuclear status.

“In the worst-case scenario, they may carry 1,286 nuclear warheads,” he said, meaning that the U.S. could nearly double the number of deployed warheads allowed by the New Start treaty.

He said “that there is almost no time left” to discuss that and other issues for the treaty to be extended by another five years as envisaged during the signing.

“It gives reason to suspect our American counterparts of setting ground to avoid those discussions … and just let the treaty quietly expire,” Ryabkov said.

Ryabkov also said Russia stands ready for talks on a possible successor to the 1987 Intermediate-Range Nuclear Forces treaty.

“We are ready for dialogue,” Ryabkov said. “If the U.S. is interested, it should spell out its proposal.”

Citing Russian violations, the U.S. on Saturday formally suspended its obligations under the INF that bans all land-based cruise and ballistic missiles with a range of 500 to 5,500 kilometers (310 to 3,410 miles), setting the stage for the treaty to terminate in six months. Russia, which has denied any breaches, has followed suit.

Russian President Vladimir Putin instructed the military over the weekend to work on developing new land-based weapons that were previously forbidden by the INF treaty, but emphasized that such new weapons won’t be deployed to the European part of Russia or any other region unless the U.S. does so in those areas.

Ryabkov expressed particular worry about U.S. plans to produce new, low-yield nuclear weapons, warning that it could dramatically lower the threshold for their use.

“It’s very alarming,” he said, adding that the plans could revive old Cold War era concepts.

“It throws us many decades back to the ideology of nuclear battlefield weapons,” he said. “There are just a couple of steps left … before the revival of nuclear artillery, nuclear mortars, nuclear mines, nuclear grenades and other things like that. It appears to reflect the eagerness of those who have grown up in the age of computer games to easily push the button.”