The official end date for the exercise is 20 September.
Since the two nations split after the break up of the Soviet Union, Belarus has struggled to maintain its sovereignty and independence in Russia's shadow, and some Western observers have warned that the Russian troops who come to Belarus for the Zapad games may wind up occupying it.
With NATO officials quoted as saying up to 100,000 troops will be involved in the "Zapad" (which means "West") exercise, it has prompted warnings on social media that Russian Federation "is mobilizing for war on a July 1914 scale". "Every nation, also Russian Federation, has the right to exercise its forces but it's important this is done in a transparent way to prevent misunderstandings, miscalculations", he said.
Russian Federation has clearly demonstrated during various snap exercises over the past several years that it can move large forces at long distances, so it would be hard to argue that additional bases in Belarus are imperative to ensure Russia's ability to project power in the West.
How many troops are participating? It also serves to validate aspects of the Ukraine's military training program. Russian Federation has said that some 12,700 troops will be involved but the actual figure is not certain. And Russian officials say no more than 13,000 troops will be involved in the drills - to which NATO observers have been invited in accordance with global treaties.
One senior European security official said Zapad would merge manoeuvres across Russia's four western military districts in a "complex, multidimensional, aggressive, anti-NATO exercise".
"There are many doubts and fears that, because of the Russian federation's previous actions, not all forces and equipment will be removed [from Belarus] after the exercise", he told reporters in Warsaw on Wednesday. Lithuania, which borders Belarus and formerly part of the Soviet bloc, is wary of the increased threat and unpredictability of Russian Federation.
In the drills, which cover a vast area from Belarus and Russia's Western borders up into the Arctic, the two countries' troops will battle a fake state invented for the goal.
U.S. tanks, combat vehicles and other military equipment have arrived in the Polish city of Gdansk as part of Operation Atlantic Resolve, a NATO exercise aimed at boosting the alliance's military presence in Eastern Europe.
NATO's easternmost members have been wary of an increasingly aggressive Russian Federation, particularly following Russia's 2014 military invasion and annexation of Crimea and Moscow's support of separatist rebels in eastern Ukraine.
With Russia's seizure of Crimea in 2014 and its intervention in Syria's war in 2015, North Atlantic Treaty Organisation is distrustful of the Kremlin's public message.
The arriving USA tanks are joining four multinational battalions recently deployed to Poland, Lithuania, Latvia and Estonia amid fears over Russian intentions throughout the region. "We are prepared as never before to react, to watch, to see what's happening behind our borders", Grybauskaite told CNBC. "They say, 'We're just doing an exercise, ' and then all of a sudden they've moved all these people and capabilities somewhere".