The Russian and Belarusian armed forces began their largest military exercise in years on September 14, putting neighbouring countries on alert. 

The week-long exercise, tellingly codenamed "Zapad", or "West", will see the two eastern armies train according to a number of strategies in a hypothetical conflict with Nato. Alliance members Poland and the three Baltic states are worried that Russia will use the exercise – which may involve up to some 100,000 troops although Moscow insists the figure is below 15,000 – to boost its military presence in the Kaliningrad region and possibly in Belarus for years to come.

Speculation also focuses on how an increased presence of the Russian military in Belarus could forestall any plans of opposition figures aimed at ousting President Aleksander Lukashenko, whose autocratic rule from Minsk dates back to 1994.

Nato has stepped up its military presence in the region in recent quarters in a show of deterrence capabilities. In response to Zapad, the US also sent a tank brigade into Poland this week which will stay for the duration of Zapad. 

Moscow interprets such moves as hostile and has reacted with a military build-up along Nato’s eastern flank. Russia has also accused Nato of hyping the dangers of Zapad in order to justify shuffling more military might over to Eastern Europe.

Russia insists the manoeuvres are routine and that the West is overstating their purpose. Nato is however concerned by the discrepancies between the official figures on involved troops and equipment and the possible scale in reality of the exercise as estimated by Western intelligence. 

Belarus has said the Russian troops will leave for Russia by the end of September.

Warsaw and the Baltic countries are naturally wary of Russia. Their concerns have remained elevated since Russia annexed the Crimean peninsula from Ukraine in 2014 in a blatant violation of international law.

Lithuania is particularly unnerved. The country is squeezed between Belarus and a strategic Russian military outpost, the Kaliningrad exclave. A border area, known as the Suwalki gap, represents a tough-to-defend flat narrow piece of land between Belarus and Kaliningrad that connects the Nato-member Baltic States to Poland. It is a recognised Nato weakness.

“The goal of the Zapad exercise is to frighten us, to break our will to defend ourselves so that we are paralyzed and can do nothing in our state," Lithuanian President Dalia Grybauskaite told reporters in Vilnius last week, according to The Baltic Times. 

The exercise “stipulates that some extremist groups have penetrated to the territories of the Republic of Belarus and the Kaliningrad region of the Russian Federation in order to carry out terrorist attacks and destabilise the Union State of Russia and Belarus,” the Russian defence ministry said in an official description of Zapad. 

The war story is that the groups are supported with logistics and equipment by the imaginary states of Vesbaria, Lubenia, and Veishnoria, located on the actual territory of Poland and Lithuania, as well as Belarus.

The goal is said to be a rehearsal of Russia’s capability to isolate the Baltic states from Nato’s help. Zapad is also supposed to give Nato strategists food for thought concerning the cost of defending the Baltic countries.

“Every nation, also Russia, has the right to exercise its forces but it's important this is done in a transparent way to prevent misunderstandings, miscalculations," Nato’s Secretary General Jens Stoltenberg told CNBC.

"And we've seen before, Russia using military exercises as a disguise for aggressive actions against other countries; that was the case in 2008 [in Georgia] and that was the case in 2014 when they annexed Crimea," Stoltenberg said.

The continuous tension between Russia and Nato – on the alliance’s eastern flank in particular – is likely to spur countries such as Poland and the Baltic trio to push for new methods to boost the response potential of Nato and the EU. A recent example is Vilnius’ idea of creating a “military Schengen”, or a mechanism for the easier movement of military forces in Europe. Efforts will also be made to tighten cyberdefence.