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.

The drills come a day after Russian President Vladimir Putin and his increasingly isolated 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.

Poland has introduced an unprecedented state of emergency along its border with Belarus following an influx of migrants that Warsaw blames on the Minsk regime.

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 presser following the talks.

The Russian leader has extended a helping hand to his Belarus ally, increasingly isolated since orchestrating a ruthless crackdown on the opposition following massive protests against him last year.

Putin and Lukashenko have sought to present a unified front in their confrontation with the West.