Speaking exclusively to CNBC on Thursday, Jens Stoltenberg, Secretary General of North Atlantic Treaty Organisation, called on Russian Federation to be "transparent" about its military exercises to avoid any "misunderstandings or miscalculations".
The exercises began Thursday night with units simulating hunting down and destroying reconnaissance agents belonging to illegal armed groups, according to Oleg Belokonev, the Belarusian Deputy Defense Minister.
What messages do the drills send?
The main goals of the drills are to "update the operational compatibility of headquarters at different levels, promote the interoperability of prospective forces and weapons control systems, test new charter documents, and allow commanders of all ranks to practice planning events of a military nature and commanding forces on the basis of modern armed-conflict experience", the statement said.
Michael Kofman with the Center for Naval Analyses said at the briefing that the joint exercises will not only show the nuts and bolts of Russia's troop placement, but also Russia's ability to intervene on Belarus' behalf if it is threatened. This was stated by President of Lithuania Dalia Grybauskaite. "And I am sure that we will restore our relationship with NATO and we will return to the wonderful form of cooperation that is the Russia-NATO Council". As of Thursday morning, Russian tank divisions said they were moving to Belarus for the exercises.
How many troops are participating?
Ukrainian President Petro Poroshenko has stepped up security on his country's border with Belarus, warning that the Zapad (West) 2017 exercises could be a prelude to an invasion.
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"People are anxious this is a Trojan horse", U.S. Army Lt. Gen.
"For Russia it would be logical to try to cut us off, which they have already practised", he said.
Moscow officials said the exercises are in no way meant to stage attacks on other places and that the West was "whipping up hysteria" over the drills, Reuters reported.
"We urge Russian Federation to share information regarding its exercises and operations in NATO's vicinity to clearly convey its intentions and minimize any misunderstandings", Pentagon spokesman US Army Lt. Col. Michelle Baldanza told CNN.
Sweden, meanwhile, is holding its own three-week military exercises in the Baltic Sea with 20,000 troops, including 1,000 US soldiers. Some NATO members, including the Baltic states and Poland, have criticized a lack of transparency about the exercises and questioned Moscow's real intentions.
"We have seen before that Russian Federation has used big military exercises as a disguise or a precursor for aggressive military actions against their neighbours", Stoltenberg said. Russian Federation had leased a naval base in Crimea from Ukraine prior to its seizure, and used troops deployed there to quickly take over the Black Sea peninsula.
"The drill is a threat to us, no matter what Russian Federation says", he told Polish TV.