MOSCOW/WASHINGTON (Reuters) – Russia and the United States on Wednesday remained at odds over extending the last major arms control pact between the world’s largest nuclear weapons powers, with Moscow denying U.S. assertions of an agreement in principle.

The New START (Strategic Arms Reduction Treaty) accord, signed in 2010, limits the numbers of strategic nuclear warheads, missiles and bombers that Russia and the United States can deploy. It expires in February.

A failure to extend the pact would remove all constraints on U.S. and Russian deployments of strategic nuclear weapons and their delivery systems, fueling a post-Cold War arms race and tensions between Moscow and Washington.

U.S. officials have indicated that an agreement to extend it has been reached in principle.

Kremlin spokesman Dmitry Peskov said on Wednesday that no deal had yet been reached despite what the Kremlin hoped was a joint understanding that the pact did need to be extended.

“As for the understanding for the need to extent the START treaty, we hope we are on the same track in this regard,” Peskov said on a conference call with reporters. “We understand that it needs to be extended, that this is in the interest of our two countries and the strategic security of the whole world.”

U.S. Secretary of State Mike Pompeo declined to comment when asked to elaborate on the agreement in principle that the top U.S. arms control negotiator, Marshall Billingslea, on Tuesday said had been reached “at the highest levels.”

“We would welcome the opportunity to complete an agreement based on understandings that were achieved over the last couple of weeks about what that range of possibilities look like for an extension of New START,” Pompeo told a State Department news conference.

He said the United States would continue the talks on the treaty, which can be extended for up to five years with the agreement of both presidents.

“I am hopeful that the Russians will find a way to agree to an outcome that frankly I think is in their best interest and in our best interest,” he said.

Pompeo reiterated a call for China to join the United States and Russia in talks on a trilateral nuclear arms control accord. China, whose nuclear arsenal is much smaller than the U.S. and Russian stockpiles, repeatedly has rejected the proposal.

Foreign Minister Sergei Lavrov said earlier on Wednesday Moscow did not see prospects for extending the new START arms control treaty with Washington but planned to continue talks nonetheless.

New START is a successor to the original agreement signed in 1991 between the then-Soviet Union and the United States.

Arms deals between President Ronald Reagan and Soviet leader Mikhail Gorbachev in the 1980s, and their successors George H.W. Bush and Russian President Boris Yeltsin in the 1990s, underscored growing trust between the superpowers and contributed to ending the Cold War.

(Reporting by Gabrielle Tétrault-Farber Anton Kolodyazhnyy in Moscow and Jonathan Landay and Humeyra Pamuk in Washington.; Editing by Andrew Osborn and Marguerita Choy)