Moscow and Minsk on Thursday launched the week-long "Zapad-2017" drill. In it, the two countries will deploy their troops, designated as "the Northern ones" to stand up to the aggression from "the Western ones" – armed attackers from the made-up countries of Vesbaria, Lubenia, and Veishnoria.

According to the scenario released by Russian and Belarusian defense officials, Vesbaria and Lubenia are located in the Baltic region and control the corridor which links the Russian exclave of Kaliningrad with Belarus. In the real world, the corridor roughly corresponds to the border between Lithuania and Poland, both of them NATO members.

Read more: Zapad war games 'peaceful and defensive' Russia assures West

The hypothetical state of Veishnoria, however, is located in the Grodno area of Belarus, near the country's western border.

Independent experts see this as a sign that Minsk and Moscow are preparing scenarios for threats originating in NATO countries as well as from within Belarus. The Grodno area seems to have a special significance as the home for a large population of Poles living in the former Soviet state. However, military officials insist that the scenario was developed "against a hypothetical opponent, unrelated to the concrete region."

What is the goal of the drill?

"Belarus and the Kaliningrad region have been infiltrated by extremist groups with the intention of committing terrorist attacks. The illegal militias are backed from abroad, providing them with armaments and naval and air capabilities. In order to neutralize the opponents, land forces will be deployed to cut off their access to sea and block air corridors in the region, with the support of the air force, air defense forces, and the navy," the official plan says.

Read more: Russia readies troops for Zapad war games with Belarus

The goal of the Zapad-2017 maneuvers is to coordinate actions between regional military commands "in the interest of ensuring military safety," Moscow and Minsk said. "The Republic of Belarus strives to prevent armed conflicts, and the Russian federation is providing it with political backing, financial aid, as well as technical and military support," according to the Belarusian Defense Ministry.

The drill is set to proceed in two stages. Initially, the military will boost their air force and air defense capabilities to protect key military and state objects, and prepare to "isolate regions of activity by the illegal armed groups and their subversive-reconnaissance squads." The second stage will be "to work out the issues of managing troops while repelling an aggression" against Russia and Belarus.

How many troops are taking part?

According to offical figures, some 12,700 servicemen are involved in the drills. "Zapad-2017" also involves 70 planes and helicopters, 280 tanks, 200 artillery weapons, ten ships, and various other pieces of military equipment. The drills include agents of the Russian intelligence service FSB, as well as people working for the Russian Foreign Ministry and the Ministry of Emergency Situations.

However, NATO allies have repeatedly disputed these numbers, with German Defense Minister Ursula Von der Leyen claiming the real number is likely to be upwards of 100,000 troops. International accords mandate that countries provide a larger degree of transparency when holding drills with over 13,000 troops.

Russia’s Defense Ministry said it was "bewildered" by Von der Leyen's assertion, and repeated its claims that drill would stay below the 13,000 threshold. Previously, the Kremlin has asked foreign defense officials and military-diplomatic corps to visit the final stage of the joint exercise at one of the sites in Russia. Belarus also stated that it had sent out invitations to UN, OSCE, NATO, the post-Soviet Commonwealth of Independent States, and military attaches accredited in Belarus.

Read more: Ursula von der Leyen says Russia showing off 'power'

Where is the drill being staged?

The bases involve seven locations in Belarus, one location in the heavily militarized Russian exclave of Kaliningrad, and two in western Russia. In order to reduce tensions with neighboring countries, the authors of the drill made an effort to pick the areas "at a significant distance from the border."

Read more: What are Russia's Zapad war games?

NATO's eastern members are concerned over the deployment of Russian troops near their territory, as Moscow has been known to stage large drills ahead of conflict in Georgia in 2008 and the annexation of Crimea in 2014. Some have even speculated that Russia might use the troops to occupy Belarus, its closest European ally. Most observers, however, consider this move to be extremely unlikely.

The drill has "strictly defensive character, its execution will not present any threat for the European community as a whole, nor for the neighboring countries," the Russian defense ministry said. The Belarusian side has ensured that after the drills are over "by September 30 the military personnel, weapons, military equipment and specialized devices of Republic of Belarus will be returned to its permanent deployment locations, and the elements of the Russian military will leave Belarusian territory."