0414 GMT December 09, 2021
The Zapad-2021 military exercises by the armies of both countries will last a week and take place in Belarus, western Russia and the Baltic Sea, the Russian Defence Ministry said.
Moscow said 200,000 personnel will take part, according to AFP.
The drills come a day after Russian President Vladimir Putin and his Belarusian ally Alexander Lukashenko said they agreed to deepen the integration of their ex-Soviet countries, including in areas of defence.
The exercises are also closely watched by Belarus's western neighbours.
Speaking in Moscow on the eve of the drills, Putin and Lukashenko said they would deepen their military ties.
The Russian leader said the drills are "not directed against anyone, but are logical in conditions when other unions – such as NATO – actively increase their military presence" on the borders of Russia and Belarus.
Lukashenko said the two countries "are not doing anything that our opponents are not".
Putin, in power for more than 20 years, and Lukashenko, in power for nearly 30, announced Thursday a range of agreements deepening their ties.
While the pair said they had focused on creating a unified economic policy, Lukashenko also said they had "progressed" on extending military ties.
"We discussed building a single defence space," Putin said at a Kremlin press conference following the talks.