Defence Minister Sergei Shoigu says the decision was taken after what he called a sharp escalation on Russia's borders.
President Vladimir Putin made the announcement in March.
He said 10 aircraft capable of carrying tactical nuclear weapons are already in Belarus, and that a storage facility will be completed by July.
It will be the first transfer of nuclear weapons to another country since the mid-1990s.

Let's speak to journalist Yulia Shapovalova in Moscow.

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