The president of Belarus announced this week that the country has received tactical nuclear weapons transported from Russia.
President Alexander Lukashenko said Monday that the intensely-regulated weapons were brought to Belarus in October.
No further information was offered on the nature of the nuclear weapons or their intended use.
Tactical nuclear weapons are smaller, short-range missiles intended for use on a battlefield.
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Lukashenko has previously suggested that nuclear weapons brought to Belarus are intended to serve as a deterrent to NATO allies.
Russia has stated that it remains in control of the nuclear weapons it provides to Belarus — its closest international ally.
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Lukashenko's claim has raised alarms in neighboring countries as Belarus' closeness with Russia has shifted the region's center of gravity toward Moscow.
Russian President Vladimir Putin signed legislation in November de-ratifying a key international nuclear weapons treaty.
The law withdraws Russia from the Comprehensive Nuclear Test Ban Treaty, originally signed in 1996 and ratified in 2000.
Russian officials have characterized the country's withdrawal from the treaty as a move toward equality with Western powers.
Just days later, the Russian military reported that it successfully test launched an intercontinental ballistic missile designed to carry nuclear warheads from a new nuclear submarine.
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The Russian Defense Ministry said in a statement that the Imperator Alexander III strategic missile cruiser fired the Bulava missile from an underwater position in Russia's northern White Sea and hit a target in the far-eastern region of Kamchatka. It was not immediately clear from the statement when the test launch occurred.
Fox News Digital's Danielle Wallace contributed to this report.