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(CNN) -- Belarusian President Alexander Lukashenko said countries that are ready to "join the Union State of Russia and Belarus" will receive nuclear weapons. The statements come days after confirming that the transfer of some tactical nuclear weapons from Moscow to Minsk has begun.

Lukashenko, a close ally of Russian President Vladimir Putin, made the comments in an on-camera interview published Sunday on state channel Russia 1.

During the interview, Lukashenko said: "No one cares that Kazakhstan and other countries have the same close relations we have with the Russian Federation."

"It's very simple," he added. "Join the Union State of Belarus and Russia. That's it: there will be nuclear weapons for everyone."

Signed in 1999, the Agreement on the Establishment of the State of the Union of Belarus and the Treaty of Russia established a legal basis for a broad alliance that encompassed the economy, information, technology, agriculture and border security, among other things, between the two countries, according to the Belarusian government's website.

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It was unclear how broad Lukashenko's invitation to join the Union State was, and he offered no further details.

But his comments about handing over nuclear weapons to like-minded allies are likely to raise concerns at a time of rising global proliferation and as Moscow threatens the world with its own atomic arsenal as its war against Ukraine falters.

On Thursday, the Belarusian autocrat said he had begun the transfer of some tactical nuclear weapons from Russia to Belarus, following an agreement signed by Moscow and Minsk.

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"It was necessary to prepare storage sites, etc. We did all this. Thus, the movement of nuclear weapons began," Lukashenko said, according to state news agency Belta.

He also promised the safety of those weapons, saying, "This is not even under discussion. Don't worry about nuclear weapons. We are responsible for this. These are serious problems. Everything will be fine here."

Putin has previously said Russia would retain control over any tactical nuclear weapons stationed in Belarus and compared the move to Washington's practice of placing nuclear weapons in Europe to prevent host countries, such as Germany, from breaking their commitments as non-nuclear powers.

Belarus has not had nuclear weapons on its territory since the early 1990s. Shortly after gaining independence following the collapse of the Soviet Union, it agreed to transfer all Soviet-era weapons of mass destruction stationed there to Russia.

Since invading Ukraine more than a year ago, Putin has used escalating rhetoric on several occasions, warning of the "growing" threat of nuclear war and suggesting Moscow might abandon its "don't be the first to use" policy.

In March, Putin said Moscow will complete the construction of a special storage facility for tactical nuclear weapons in Belarus in early July, and said Russia had already made the transfer to Belarus of an Iskander short-range missile system, which can be equipped with nuclear or conventional warheads.

Tactical nuclear weapons are smaller than strategic nuclear weapons, which can decimate entire cities, and are designed to be used on a limited battlefield. However, their explosive yields are still sufficient to cause great destruction and radiation contamination.

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Strong condemnations

The United States and the European Union, as well as opposition leaders in Belarus, have denounced the move to deploy Russian tactical nuclear weapons in Belarus.

"It's the latest example of irresponsible behavior we've seen from Russia since its full-scale invasion of Ukraine more than a year ago," U.S. State Department spokesman Matthew Miller said Thursday.

Miller added that despite the report of the transfer, the United States sees "no reason to adjust our strategic nuclear posture" and said there are "no indications that Russia is preparing to use a nuclear weapon."

The European Union called the agreement between Moscow and Minsk "a step that will lead to an extremely dangerous escalation."

And Ukrainian presidential adviser Mykhailo Podolyak tweeted Sunday that Lukashenko's words "directly indicate that the Russian Federation is deliberately 'killing' the concept of global nuclear deterrence and 'burying' the key Global Treaty on the Non-Proliferation of Nuclear Weapons."

"This fundamentally undermines the principles of global security," Podolyak said. "There can only be one solution: a tough stance by the nuclear states; relevant UN/IAEA resolutions; sweeping sanctions against (Russian state nuclear energy company) Rosatom; systemic financial sanctions against Belarus and, ultimately, against Russia."

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Belarusian opposition members also criticized the deal, with exiled opposition leader Sviatlana Tsikhanouskaya saying in a post on Twitter that "we must do everything possible to prevent Putin's plan to deploy nuclear weapons in Belarus."

"It directly violates our non-nuclear constitutional status and would ensure Russia's control over Belarus for years to come. And it would further threaten the security of Ukraine and the whole of Europe," he said.

Analysts say there are still many unknowns with the transfer.

"We don't know if he has already started physically, although Lukashenko says he has. We don't know if any weapons have actually left Russia yet, we don't know when they will be deployed, we don't know what kind of weapons will be deployed," national security expert Joe Cirincione told CNN on Friday.

Cirincione, former president of the Ploughshares Fund, which focuses on reducing the threat of nuclear weapons, said that going ahead would be "a historic milestone."

"We can't recall another incident where, during a crisis, a nuclear-armed state took its weapons out of the garrison and put them in the field, which is effectively what Putin is doing here," he said.

-- CNN's Lauren Kent, Xiaofei Xu and Radina Gigova contributed to this report.

Alexander LukashenkoNuclear weaponsBelarus