The United States has seen no indication that Russia has yet moved any nuclear weapons, National Security Council spokesman John Kirby said Sunday, after Moscow announced it would station tactical nuclear arms in Belarus.

President Vladimir Putin's announcement on Saturday that Russia would station tactical nuclear weapons in neighbor and ally Belarus sparked condemnation from the international bodies and Ukraine, which Moscow invaded last February.

"We have not seen any indication that he (Putin) has made good on this pledge or moved any nuclear weapons around," Kirby told CBS's "Face the Nation."

With fears of a nuclear war rising since the Russian invasion of Ukraine, experts believe that any strike carried out by Moscow would likely involve small-size battlefield weapons, called "tactical" as opposed to "strategic" high-powered long-range nuclear weapons.

Kirby said, however, that Washington has "seen no indication he has any intention to use nuclear weapons, period, inside Ukraine."

The United States monitors the situation daily, he added, but that so far there was "nothing that would cause us to change our own strategic deterrent posture."

Putin said the deployment was similar to moves from the United States, which stores such weapons in bases across Belgium, Germany, Italy, the Netherlands and Turkey, an analogy western allies called "misleading".

Russia is due to start training crews on April 3 and plans to finish the construction of a special storage facility for tactical nuclear weapons in Belarus by July 1.

Kyiv on Sunday said it was seeking an emergency meeting of the United Nations Security Council over the announcement.

The NATO alliance branded the move as "dangerous and irresponsible."