Putin has several times referred to nuclear weapons since his country invaded Ukraine on February 24 in what the West has seen as a warning not to intervene.
Russia will supply Belarus with missiles capable of carrying nuclear warheads after the president complained about nuclear-armed NATO flights coming close to the Belarusian border.
President Vladimir Putin made the announcement on Saturday as he received Belarusian leader Alexander Lukashenko in Moscow.
“In the coming months, we will transfer to Belarus Iskander-M tactical missile systems, which can use ballistic or cruise missiles, in their conventional and nuclear versions,” Putin said in a broadcast on Russian television at the start of his meeting with Lukashenko in St Petersburg.
At the meeting, Lukashenko expressed concern about the “aggressive”, “confrontational”, and “repulsive” policies of Belarus’s neighbours Lithuania and Poland.
He asked Putin to help his country mount a “symmetrical response” to what he said were nuclear-armed flights by the US-led NATO alliance near Belarus’s borders.
Putin offered to upgrade Belarusian warplanes to make them capable of carrying nuclear weapons amid soaring tensions with the West over Ukraine.
Last month, Lukashenko said his country had bought Iskander nuclear-capable missiles and S-400 anti-aircraft anti-missile systems from Russia.
“Many Su-25 [aircraft] are in service with the Belarusian military. They could be upgraded in an appropriate way,” Putin said.
“This modernisation should be carried out in aircraft factories in Russia and the training of personnel should start in accordance with this. We will agree on how to accomplish this.”