Russia on Monday challenged the U.S. claim that it has fulfilled its obligations under a pivotal nuclear arms deal, a new argument that could further fuel tensions between Moscow and Washington.

The Russian Foreign Ministry said it “can’t confirm” the latest U.S. State Department data indicating that the U.S. has complied with the thresholds set by the 2010 New START treaty. It limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers.

The ministry said the U.S. removed 56 Trident II submarine-launched intercontinental ballistic missiles and 41 B-52H strategic bombers from its count of nuclear arsenals after re-equipping them to carry conventional weapons.

But it argued that the U.S. had failed to let Russia verify the move in line with the treaty, and failed to list four land-based missile silos converted for training purposes — a move Russia said didn’t conform to the treaty.

The ministry said the perceived U.S. breach of the treaty’s limits was “unacceptable,” adding that it expects Washington to “show a constructive approach to settling that acute issue.”

The tough statement marked the first time Russia raised the issue of the alleged U.S. non-compliance with the pact signed by President Barack Obama and then-Russian President Dmitry Medvedev amid a brief thaw in Russia-U.S. ties. The New Start came into effect in 2011 and is to expire in 2021 unless the two countries extend it.

Officials in both Russia and the U.S. have given mixed signals about the pact’s future.

Russia-U.S. ties have sunk to their lowest levels since the Cold war times over the Ukrainian crisis, the war in Syria, the allegations of Russian meddling in the 2016 U.S. presidential election and alleged Russian hacking of world anti-doping bodies, athletes, plane investigations and chemical weapons probes, among other disputes.

In the arms control sphere, Moscow and Washington also have been at loggerheads over another arms control treaty — the 1987 Intermediate-range Nuclear Forces Treaty.

The U.S. has accused Russia of deploying a new type of missile in violation of the pact that bans an entire class of weapons — all nuclear and conventional ground-launched ballistic and cruise missiles of intermediate range. Russia has rejected the accusations.

(AP)