"They continually send more troops than they report to the international community," the official said, adding that they need to be honest about their intentions to avoid misunderstandings. For comparison, last year 24 NATO members held a military exercise named "Anakonda," which included more than 31,000 service members.
But NATO members and Western military experts believe as many as 100,000 troops may be involved in the drills. Analysts don't believe that Russia is about to launch a war.
Dubbed Zapad, which means "west" in Russian, the exercise has its roots in vast Soviet drills dating to the 1980s. "NATO remains calm and vigilant, and committed to keeping Estonia and all our allies safe," NATO Secretary General Jens Stoltenberg said last week in Estonia, one of the tiny Baltic nations that borders Russia and often worries about undue influence from Moscow. In Lithuania, another Baltic nation that was once part of the Soviet Union, Defense Minister Raimundas Karoblis summed up the mood. There is a large foreign army massed next to Lithuanian territory," he told Reuters. Ben Hodges, have raised concerns that Russia might use the drills as a "Trojan horse" to make incursions into Poland and Russian-speaking regions in the Baltics.
"There's always a possibility for miscalculation when that's going on," Gen. Scaparrotti, NATO's supreme allied commander, told reporters last month, referring to these near-misses.
"I think that's the importance of transparency, particularly on Russia's part, to tell us about [the Zapad] exercise: What should we expect to see, what is the size of them, where will they operate?
"Russia is not organizing defensive operations but instead an offensive threat, testing how serious we are about protecting the members of NATO," said Jonathan Eyal, international director of the Royal United Services Institute, a London-based think tank.
Belarus not only borders Russia, but also three of America's key but relatively isolated NATO allies: Poland, Lithuania, and Latvia.
One theory is that this year's drill could be used by Russia to "leave troops behind" in Belarus in order to give Moscow a more-advanced forward base in Europe, according to Giles at Chatham House.
If you've never attended a military ball, you're probably worrying over what to wear, how to act, what traditions to follow and what to expect.
The Vienna Document of 2011 is an agreement by members of the Organization for Security and Co-operation in Europe — a group that includes Russia — which says that any exercise involving more than 13,000 personnel must allow observers from all other OSCE nations.
Russian officials, such as Foreign Minister Sergey Lavrov, are adamant they have nothing to hide.
Other Western officials, including the head of the U. Hodges made the comment in a Reuters interview in July.