Russia starts big war games along its border, alarming its neighbors Russia's drills are some of its largest since the Cold War, according to NATO.

 -- Russia has begun war games along its western border — some of its largest since the end of the Cold War — stoking fears among its neighbors.

The exercises that Russia is conducting, with its Eastern European ally Belarus, have attracted intense attention amid nervousness over Moscow’s recent military adventures and its tensions with the West.

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 fake states invented for the purpose. As of Thursday morning, Russian tank divisions said they were moving to Belarus for the exercises.

Moscow has insisted that the long-planned drills, which it is calling Zapad 2017, are defensive and relatively small, involving only about 12,000 troops. That is just below the level at which Russia and Belarus would be required under an international convention to invite Western observers.

But the United States and NATO say the real number of troops involved is likely far higher and may be as high as 100,000.

That many troops would make these war games among the biggest since the Soviet period, and the discrepancy in reports on the size has set off concerns among some about the drills’ real purpose and, in more alarmist quarters, even fears of invasion.

The exercises, a variant of Soviet drills during the 1970s, were revived on a large scale by President Vladimir Putin in 2009. Since then, they take place every four years and have been viewed as relatively routine.

But Russia’s covert annexation of Crimea in 2014, which was masked by military exercises, has changed perspectives.

“People are worried this is a Trojan horse,” U.S. Army Lt. Gen. Ben Hodges, the commander of Army forces in Europe, told Reuters in July about fears around the Russian war games. “They say, ‘We’re just doing an exercise,’ and then all of a sudden, they’ve moved all these people and capabilities somewhere.”

Hodges and other U.S. and European officials have stressed that the current exercises are probably just drills.

“It is a provocative place and a provocative size, but I think we all understand that militaries are going to conduct military exercises,” Kurt Volker, the U.S. envoy on the Ukraine conflict, told BBC Radio on Thursday.

War games are frequently conducted around the world, including by the U.S., which this summer helped lead a NATO exercise involving 25,000 troops in Eastern Europe that practiced defense against a Russian attack. Moscow criticized those exercises as a threat.

Russia has rejected NATO’s claims that tens of thousands of troops will take part in its current war games, insisting that it will be abide by the so-called Vienna Document, which requires that any exercise involving more than 13,000 troops be open to foreign observers.

NATO officials said Russia has a long history of lowballing troop numbers. Estonia’s Defense Minister Margus Tsahkna pointed to a document showing that Russia’s military has requisitioned over 4,000 railcars for the war games, suggesting that the number of troops who will be traveling will be far more than the 12,700 Moscow says are taking part.

The worry over the exercises underlines the suspicions over Russian military intentions since its invasion of Ukraine three years ago.

“We can’t be totally calm. There is a large foreign army massed next to Lithuanian territory," Lithuania’s Defense Minister Raimundas Karoblis told Reuters recently.

Adding to the discomfort is one of the games’ scenarios: a Russian response to aggression from a fictional Western-backed country. In August, Belarus’ Defense Ministry revealed that its and Russia’s troops would be repelling the forces of a fake state, Veishnoriya, supported by unspecified foreign backers, widely understood to be stand-ins for NATO and the U.S.

For some, that sounds uncomfortably like rehearsing for NATO’s nightmare scenario of a Russian tank rush into the Baltic states. The participation of an armored force, the 1st Armored Guards Army, which Western planners view as a massive offensive fist, has prompted further skepticism that the exercises will run only defensive practices.

Perhaps the most plausible scenario worrying Western military planners is that the thousands of Russian troops moving into Belarus for the exercises will never go home.

Belarus, a former Soviet satellite often called Europe’s last dictatorship, has long maintained a delicate balancing act by trying to preserve a measure of independence while remaining closely integrated with its giant neighbor. But a quarrel over gas supplies and Russia’s invasion of Ukraine have recently strained that balance. With Russian troops already based in Belarus, some analysts and opposition figures in the country have suggested that the Kremlin might seize the opportunity to expand its armed presence there.

The governments of Belarus and Russia have dismissed that idea. And jokes have sprung up around the notion of a looming invasion by the fictional Veishnoriya. A satirical Twitter account purporting to represent Veishnoriya’s foreign ministry has posted menacing messages warning that it is building up its troops along its border with Belarus.

Another group on Russia’s equivalent of Facebook has started posting tourism advertisements for the invented nation.