Russia and Belarus launched joint military drills on Thursday despite concerns in western countries that Moscow is plotting a major escalation of the conflict in Ukraine.
The exercises, scheduled to continue until February 20 in Belarus, centre around "suppressing and repelling external aggression," Russia's defence ministry said.
Soldiers would practise beefing up sections of the Belarus border to block the delivery of weapons and ammunition into the country, among other scenarios, it said.
The exercises have exacerbated deeply strained ties between Russia and the West, which accuses Moscow of massing approximately 100,000 troops around the borders of Ukraine for a potential invasion.
British Foreign Secretary Liz Truss was in Moscow on Thursday for talks with her Russian counterpart to urge the Kremlin not to attack or face "massive consequences" from western sanctions.
Moscow and Minsk have not disclosed how many troops are participating in the drills, but the United States said Russia was planning to dispatch 30,000 troops to several regions in ex-Soviet Belarus.
Responding to western concerns, the Kremlin insisted it has no intention of leaving the troops permanently on Belarusian territory.