Russia's huge military exercise along its western border this week has increased nervousness among neighboring countries as well as straining relations with NATO.
The "Zapad 2017" military exercise, running from the 14th until the 20th September, is held every four years and will on this occasion include activities on the borders of Poland, Lithuania, and Belarus.
The main purpose of Zapad, which literally means west, is to simulate defense and counter-attack in case of war with NATO member countries.
Security expert Otilia Dhand at Teneo Intelligence told CNBC Wednesday that while similar exercises have happened regularly since 1999, tension is enhanced this time because of recent history.
"Since the last Zapad exercises in 2013, Russia has annexed Crimea and fomented unrest in eastern Ukraine, where the conflict is ongoing.
"The Baltic members of NATO are therefore especially concerned over the possibility that these exercises may involve incursions into their territorial waters and airspace, as well as provide cover for building up Russian forces at bases close to their borders," she said.
Since 2014, and the fall of Ukrainian President Viktor Yanukovych, Russian-backed soldiers have taken control of strategic positions within the Ukrainian territory of Crimea.
Dhand said that this week's exercises could allow Moscow to funnel more equipment to separatist factions installed in eastern Ukraine.