Russia is in the middle of one of its biggest military exercises since the end of the Cold War: Zapad 2017.

From September 14 to 20, the Russian and Belarusian militaries are holding a joint war game to simulate fending off an attack from Western powers. Russia says only 12,700 troops — as well as 70 planes and helicopters, 280 tanks, 200 artillery weapons, and 10 ships — are participating in the drills.

But foreign officials, including German Defense Minister Ursula von der Leyen, believe the number is closer to 100,000. That’s significant because if a military exercise involves 13,000 troops or more, then foreign officials must be formally invited to watch, according to an international agreement — and the 12,700 number is suspiciously just under that mark.

Western leaders are especially worried about the exercise. NATO accused Russia of using the last Zapad drills in 2013 to prepare for its invasion of Ukraine the following year. Now some leaders, such as Lithuania’s Defense Minister Raimundas Karoblis, fear having Russian troops amassed near NATO territory. "We can't be totally calm. There is a large foreign army massed next to Lithuanian territory," Karoblis told Reuters.

Russia, however, denies that charge. Zapad, which translates to “West” in Russian, is "strictly defensive [in] character, [and] its execution will not present any threat for the European community as a whole, nor for the neighboring countries," according to the Russian defense ministry.

The United States is watching the exercise with interest too, as Russia’s show of power comes at a time of high tension between Washington and Moscow.

The photos below, which show a line of tanks, missile firings, and helicopters dropping fake ordnance, likely won’t help calm any nerves.