"By turning Belarus into its nuclear staging ground near NATO borders, the Kremlin is de facto legitimising the proliferation of nuclear weapons worldwide and setting a dangerous precedent for other authoritarian regimes," the ministry said in a statement.
Belarus said on Monday its armed forces had begun training exercises involving Russian nuclear weapons.
"During the training, in co-operation with the Russian side, it is planned to practise the delivery of nuclear munitions and their preparation for use," the Belarusian defence ministry said.
It said the exercise would test the military's readiness to deploy nuclear weapons in different areas of the country.
Belarusian President Alexander Lukashenko agreed in 2023 - a year after Russia's invasion of Ukraine - to host Russian tactical nuclear missiles.
Russian President Vladimir Putin has made clear that Russia retains control of their use.
Ukraine on Monday urged its allies to tighten sanctions against Russia and Belarus over the development: "Such actions must face unequivocal and resolute condemnation from all states that respect the nuclear non-proliferation regime."
Belarus - which shares borders with Russia, Ukraine and three NATO members - said the exercise was not aimed against any other country and did not pose security threats in the region.
Meanwhile, Russian authorities voiced concern over what they described as Ukrainian attacks near the Russian-occupied Zaporizhzhia nuclear power plant in southeastern Ukraine, warning of escalating risks at the site.
Alexei Likhachev, head of the Russian state nuclear company Rosatom, said the situation around the plant was becoming increasingly dangerous.
"We are getting closer to a point of no return."
Russian forces took control of the facility shortly after the invasion of Ukraine began more than four years ago.
Russia has since accused Ukraine of repeated artillery and drone strikes in the surrounding area.
Likhachev said the situation amounted to "playing with fire" and warned of potential consequences for all of eastern Europe.
He urged international efforts, including from Europe, to help de-escalate tensions around the site.
He noted about 2600 tons of nuclear fuel are stored at the plant.
In the event of a direct hit, particularly on spent fuel storage facilities, there are risks of regional significance, he said.
Attacks on facilities in the surrounding area amount to "an escalation of the situation to the point of catastrophe," Likhachev said.
According to Russian reports, several buses were damaged or destroyed in an artillery strike on a vehicle depot at the site over the weekend.
Zaporizhzhia is Europe's largest nuclear power plant, with six reactors and a capacity of about 6000 megawatts.
It is not currently generating electricity.
The International Atomic Energy Agency maintains a permanent monitoring mission at the facility to reduce the risk of a nuclear accident.
with DPA
