Ukraine and Western nations are slamming Russia's plan to deploy tactical nuclear weapons to Belarus.

Russian President Vladimir Putin announced on Saturday that a storage facility for such weapons is scheduled to be constructed in Belarus by July 1.

The Ukrainian foreign ministry condemned Putin's plan on Sunday, calling it another provocative step by his administration.

NATO also said in a statement that the Russian president's nuclear rhetoric is "dangerous and irresponsible."

Putin announced the deployment as some experts say Russian forces are losing momentum in the fierce battle over control of eastern Ukraine's Bakhmut.

A spokesperson for Ukrainian forces in the region said on Sunday that the number of Russian attacks in the city has dropped in the past two days.

The Institute for the Study of War, a US think tank, assessed on Sunday that Russian forces have continued attacking Bakhmut, but only made "marginal gains."

Russian Security Council Secretary Nikolai Patrushev, a close aide of Putin, said NATO countries are a party to the conflict in Ukraine, in an interview with Russian media released on Monday.

Patrushev also said that NATO does not conceal its primary objective, which he said is Russia's defeat on the battlefield and its subsequent "dismemberment."