Russia on Thursday kicked off a week of war games with its ally Belarus that have NATO neighbors and the United States watching anxiously, even as they give Moscow the chance to flex its muscles against one of its primary fears — possible political fissures in the Kremlin's own orbit.

Moments after Russia’s defense ministry said the war games dubbed “Zapad 2017,” or “West,” had begun, it announced that elements of its First Tank Army had been “put on alert” and moved into Belarus for the exercise. Airborne units stationed in Russia also were mobilized and prepared to join the drills, the ministry said.

At a time of renewed Cold War-style tension between Russia and NATO, the symbolism couldn’t have been more striking. The Soviet-led Warsaw Pact once used the Zapad exercises to prepare for potential war with the West. The job of the Soviet tanks was to smash through NATO lines, including the 300,000 U.S. troops once stationed in Europe.

The U.S. force in Europe is down to 30,000 now, and many countries that once formed the Soviet bloc have since become members of NATO.

But Russia sees itself hemmed in by a hostile, expanding force, and Russian President Vladimir Putin has vowed to prevent revolutions in the former Soviet region similar to the 2014 rebellion that established a pro-Western government in Ukraine.

The scenario Russian and Belarusan forces are playing out involve a "Western coalition" of imaginary  states: Lubenia, Vesbaria and Veishnoria, in which Russian and Western observers see similarities to NATO members Poland, Lithuania and Latvia. In the war game scenario, the three enemies are attempting to change the regime in Belarus's capital, Minsk; turn Belarus against Russia; and annex parts of Belarus to Veishnoria.

The first phase of the drills pits Russian and Belarusan forces against “illegal armed formations” and “saboteur groups” of the Western coalition that have infiltrated Belarus.

The Russian announcement that the games had begun was accompanied by the reassurance — repeated by Moscow for weeks — that the exercise is “of an entirely defensive nature and is not aimed at any other states.”

Concerns in the Western alliance were raised by the apparent difference between official Russian figures about the size of the exercise — 12,700 troops, 138 tanks, 40 jets and helicopters — and Western estimates, based on troop and equipment movements, that the number could range from 70,000 to as many as 100,000 participants.

NATO Secretary General Jens Stoltenberg told The Washington Post last week that Russia could build trust and head off possible accidents by being more transparent.

Western military officials have expressed concern that Zapad 2017 will serve as a "Trojan horse," allowing Moscow to leave behind some of the military personnel and equipment it deployed for the drills.

The last time Russia held a Zapad drill, in 2013, it used some of the forces involved to capture the Crimean Peninsula from Ukraine the next year. No one in NATO expects anything like that to happen this time.

But senior officials in the Baltics last week said they saw the games as a rehearsal of the capability to seal off Lithuania, Latvia and Estonia and to deny access to the Baltic Sea to NATO forces attempting to come to their rescue. They also see a larger strategic goal: to demonstrate to U.S. and NATO leaders the high cost of defending the Baltics and thus bringing into question the viability of the alliance.

NATO, which conducted its own exercises involving 25,000 service members from 20 nations in Europe this summer, has stationed four battalions — including U.S. troops — in the Baltic states and Poland. Ukraine, locked in a conflict with Russia-backed separatists, is conducting its own military exercises, called "Unflinching Tenacity," and neutral Sweden has begun exercises with NATO that involve 19,000 troops.

Russian leaders have decried the criticism of their drills while allegedly larger exercises are being held outside their borders as an example of Western hypocrisy. Putin’s spokesman, Dmitry Peskov, on Thursday accused the West of “whipping up hysteria” over the war games.

“We reject complaints of these exercises not being transparent,” Peskov told a conference call with reporters.

In Minsk, Col. Vladi­mir Makarov, a Belarusan military spokesman, said that all 3,000 Russian military personnel in the country would leave when the war games conclude Wednesday.

Critics of President Alexander Lukashenko, whose rule since 1994 once earned Belarus the nickname "Europe's last dictatorship," remain suspicious.

"This is a threat to us, because they are dragging Belarus into this hybrid war, they are on our land practicing fighting a war with NATO, and we don't need that," said Nikolai Statkevich, a leader of protests against the exercises in Minsk last weekend. A former presidential candidate, Statkevich served a number of years in prison after being detained in 2011.

In Moscow’s view of an unfriendly Europe, Belarus plays a critical role, both as a buffer state and “a staging area for an attack against the West,” said Pavel Severinets, who was imprisoned from 2011 to 2013 for his role as an opposition leader.

“For the Kremlin, Belarus is the key that they will not give away,” Severinets said.

Lukashenko brought his nation of 9.5 million into close orbit with Russia, in return for subsidies and a large chunk of its trade. But the Belarusan leader has irked Moscow in recent years with efforts to forge a foreign policy independent of Moscow's. He has tried to cast Belarus as a "donor of security," a neutral country that would help others resolve crises.

Belarus voted against Russia's annexation of Crimea in the United Nations. Moscow was unhappy to learn that Ukrainian tanks fighting its proxies in the breakaway eastern provinces of Ukraine were running on fuel from Belarusan refineries that had been provided by Russia, said Andrei Porotnikov, project manager of Belarus Security Blog. Russia protested when Lukashenko decided to allow visa-free entry to tourists from 80 countries, including the European Union and the United States, as long as they stayed fewer than five days.

One goal of the Zapad exercise is to ensure that Belarus stays firmly in Moscow’s orbit, he said.

The very fact of the Zapad 2017 exercises has dealt a blow to Belarus as a “donor of security,” said Valery Karbalevich, a political analyst and author of a book about Lukashenko. The West, whose favor Lukashenko has been trying to curry, considers Russia an aggressor in Ukraine, a meddler in elections and an overall troublemaker.

“The ally of a country that is seen as an aggressor can’t be a peacemaker,” Karbalevich said.

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