Keir Giles is a senior consulting fellow the Russia and Eurasia program at Chatham House . He is also a director of the Conflict Studies Research Centre , a group of subject matter experts in Eurasian security. The opinions in the article belong to the author.

The two countries' Western neighbors have been worried. Zapad is Russian for "West," and of all the different major exercises in the Russian military calendar, it causes the most excitement and concern because it is the one that most closely resembles practice for war with NATO.

As a result, this regular event receives a lot more attention than other Russian manoeuvers of similar size. Held every four years, the exercise can even develop its own mythology: Much of the Western coverage said that the 2009 exercise ended with a simulated nuclear attack on Warsaw, Poland , even though there is no evidence at all from unclassified sources to suggest this was the case.

What happens during this year's Zapad exercise is important. The United States, NATO and especially the front-line states bordering Russia will be watching closely to learn what they can about the latest Russian capabilities and military procedures.

An additional cause for concern is that Russia has previously used the fact of large numbers of troops being on the move for major exercises to launch real military operations -- against both Georgia and Ukraine.

In Poland, Lithuania and especially Ukraine, some fear this year's Zapad could provide cover for preparing another Russian military adventure.

But unlike those exercises, Zapad is not a purely Russian undertaking. It is run in cooperation with Belarus.

Belarus finds itself in the difficult position of being officially an ally of Russia's but not sharing Moscow's antagonism toward the West and wanting instead to remain neutral in the confrontation between Russia and NATO.

But at the same time, the country shares NATO's concern about the danger of inadvertent conflict in the region, and is looking for ways to avoid inflaming the situation.

Belarus is pushing for openness to the West during the exercises -- which will also help ensure that Russia does not take the opportunity to deviate from the exercise scenario to launch some kind of unfriendly action.

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That may not have pleased Moscow, which is keeping quiet about the much bigger Zapad-related activities on its side of the border. But all these Russian activities will be far less visible to the West than the high-profile "main event" in Belarus.

At the less dramatic end of the scale, another suggestion is that Russian troops taking part in the exercise on the territory of Belarus could remain there at the end of the exercise

There has been little public discussion on what the "staying behind" option might actually look like. While major Russian units remaining on Belarusian territory seems a remote prospect, another possibility that has been put forward is Russian military equipment being left there without troops, as part of pre-positioning for possible future Russian military action launched against neighbors such as Lithuania or Poland, or the so-called Suwałki gap, from Belarus itself.

A move such as this could be portrayed by Russia as a defensive measure in response to NATO's placement of a small number of additional troops in the Baltic states and Poland under the "enhanced forward presence" program -- the argument would be that NATO has prepositioned its forces in the front-line states, so Russia is now doing the same.

But this too would require cooperation and agreement from Minsk, which does not fit with Belarus' track record of resisting attempts at increasing the amount of Russian military infrastructure in the country.

At the same time, Russia has good reason at the moment to play down conflict instead of launching new military adventures. With a strong interest in rolling back sanctions imposed by the United States and Europe, Moscow could choose to act calmly to defuse anti-Russian rhetoric and undermine those who warn of the Kremlin's aggressive intent.

As a result, Russia is currently mixing threatening language designed to intimidate the West with another, contradictory message: that those who fear a Russian military threat are "hysterical," "living in the last century," and hankering for the Cold War. By keeping quiet about Zapad, Russia allows speculation and hype in Western media -- and even from government officials -- do this job for them.

With the current level of Western alarm at possible developments of the upcoming exercise, if Zapad comes to an end with no incident, then Moscow can quite readily say, "We told you so."