Russia is about to kick off a major military exercise called Zapad on Thursday, which has some worried that it could be a “Trojan horse.”

The New York Times reported in late July that 60,000 to 100,000 Russian troops would be sent to Belarus and western Russia for the exercises scheduled for Sept. 14-20. And in May, the Washington Post cited US military estimates of 70,000 to 100,000 as taking part in the exercises.

The Economist even cited NATO estimates in August of more than 100,000, and many US generals and western politicians, including Estonia’s defense minister, have also expressed concern that Russian troops might permanently stay in Belarus.

“People are worried this is a Trojan horse,” US Army Gen. Ben Hodges told Reuters in July. “They say, ‘We’re just doing an exercise,’ and then all of a sudden they’ve moved all these people and capabilities somewhere.”

But Dmitry Gorenburg, a senior research scientist at CNA, wrote in The National Interest that these reports were “panicked accounts.” Olga Oliker, a senior adviser and director of the Russia and Eurasia Program at The Center for Strategic and International Studies, also told Business Insider that she agreed with Gorenburg’s take.

The Pentagon did not respond to a request for comment.

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In reality, the Zapad exercises, which were also held in 2009 and 2013, take place every 4 years. For the 2013 exercises, western officials estimated that 70,000 Russians participated.

Part of the reason for these disparities in estimations, Gorenburg said, is because Moscow claims the number of troops will be less than 13,000 in 2017, but there is disagreement over whether to count civilian officials and security agents as part of the overall number.

Russia may also conduct smaller exercises in the area that are not technically part of Zapad.

There’s also a tendency for the west to count full units as having participated in the exercises when in fact only parts of units were there, Gorenburg said.

Either way, that “100,000 figure is pretty off the wall,” Mark Galeotti, a senior research fellow at the Institute of International Relations Prague, told Business Insider in an email.

These “panicked accounts” all stemmed from reports about Russia using 4,000 train cars to transport troops back and forth from the exercises, which could indicate those large western estimates.

Foto: Russian servicemen march during the Victory Day parade in Moscow’s Red Square May 9, 2014. source Sergei Karpukhin/REUTERS

But Sim Tack, a Stratfor analyst, told Business Insider that estimates of 100,000 or more Russian troops were taken from a Ukrainian blog, informnapalm.org, which is run by amateur journalists. Gorenburg also told Business Insider that these concerns from western officials came largely from the Ukrainian blog.

“A lot of people have just copied that [Ukrainian blog],” Tack said, which Estonia’s Defense Minister Margus Tsahkna first started spreading.

“I don’t know [the Ukrainian blog’s] exact calculations, they just threw out the 100,000 number,” Tack said, adding that they basically figured Moscow would pack each rail cars to the brim with 72 soldiers, and that they multiplied the final number by 1.5 times on the assumption that the Kremlin was keeping the real number of rail cars secret.

Gorenburg also said that, while the famed Russian 1st Guard Tank Army was reported to be participating in 2017, Russian officials have yet to confirm it. Tack said that the tank army would partake in the exercises, but it would only be a small contingent of the corps-sized force.

In any event, “it’s hard to know how many troops will be in the [2017 Zapad exercises]” because of the disagreement over who should be counted, Galeotti said.

“What we do know is that the total number of Russian troops on Belarusian territory is not expected to exceed 3,000 personnel,” Gorenburg wrote, and “the likelihood of this exercise serving as cover for some larger nefarious aim, whether it is an attack on Ukraine or Lithuania or a stealth occupation of Belarus, is practically zero.”

It’s “highly unlikely the Russians would park troops in Belarus uninvited,” Galeotti said. “Minsk has already made it clear that it would not welcome this,” and Moscow doesn’t have the budget to maintain troops there.