Belarus has consented to let Russia station tactical nuclear missiles there.
The action formalises an agreement that Belarus President Alexander Lukashenko and Russian President Vladimir Putin reached earlier this year.
Putin has regularly vowed to defend Russia’s “territorial integrity” with nuclear weapons since the invasion of Ukraine last year.
Ukraine said Belarus had been ‘held hostage’ by the Kremlin when the arrangement was first revealed back in March.
Speaking in Minsk, Russia’s defence minister Sergei Shoigu said: ‘In the context of an extremely sharp escalation of threats on the western borders of Russia and Belarus, a decision was made to take countermeasures in the military-nuclear sphere.’
He said Moscow will retain control over the weapons and any decisions on their use.
Russian news agency TASS quoted him as saying Iskander-M missiles, which can carry conventional or nuclear warheads, had been handed to the Belarusian armed forces, and some Su-25 aircraft had been converted for the possible use of nuclear weapons.
‘Belarusian servicemen have received the necessary training in Russian training centres,’ Shoigu added.
No detail was announced regarding when the weapons would be deployed in Belarus, but Putin previously said that the construction of storage facilities would be completed by July 1.
Exiled Belarusian opposition leader Sviatlana Tsikhanouskaya condemned the move.
‘We must do everything to prevent Putin’s plan to deploy nuclear weapons in Belarus, as this will ensure Russia’s control over Belarus for years to come,’ Tsikhanouskaya said.
‘This will further jeopardize the security of Ukraine and all of Europe.’
Independent Belarusian military analyst Aliaksandr Alesin said about two-thirds of Russia’s arsenal of medium-range nuclear-tipped missiles were held in Belarus during the Cold War, adding that there are dozens of Soviet-era storage facilities that could still be used to store such weapons.
Soviet nuclear weapons stationed in Belarus, Ukraine, and Kazakhstan were moved to Russia in a US-brokered deal after the dissolution of the Soviet Union in 1991.
‘Documents in Minsk on the return of nuclear weapons were defiantly signed just at the moment when Ukraine declared a counteroffensive and Western countries are handing over weapons to Kyiv,’ Alesin said.
‘This Belarusian nuclear balcony should spoil the mood for politicians in the West, since nuclear missiles are capable of covering Ukraine, all of Poland, the Baltic States, and parts of Germany.’
Russia and Belarus have an alliance agreement under which the Kremlin subsidises the Belarusian economy, via loans and discounted Russian oil and gas.
Moscow used Belarusian territory as a staging ground for invading neighbouring Ukraine and has maintained a contingent of troops and weapons there.