Workers drill a hole for a fence near the Sudargas border crossing point with Russia in Ramoniskiai, Lithuania June 5, 2017. Thomson Reuters

The looming joint military exercise between Russia and Belarus, expected to involve about 100,000 troops, has been met with unease in Eastern Europe.

That feeling is particularly strong in the Baltic states, where relations with Russia have grown more contentious in recent months.

Lithuania, which borders Belarus and Russia's semi-exclave on the Baltic Sea, Kaliningrad, is particularly warily.

Moscow deployed nuclear-capable missiles to Kaliningrad last year and will send fighter-bomber jets and naval ships by the end of this year.

Vilnius announced in January that it would reinforce its Kaliningrad border with a static barrier: a 6-foot-high fence alongside the Ramoniškiai border crossing. Built with NATO funds, the barrier will sit opposite a barbed-wire fence built by Russia five years ago. Construction started in June and is supposed to be finished by end of this year.

Lithuanian opposition leaders have rejected the structure as a waste of money. "What can we avoid? Tanks? Of course not," an opposition parliamentarian told The Guardian. (Interior Minister Eimutis Misiunas admitted as much earlier this year.)

Locals also expressed no faith that the fence would stave off a Russian invasion. "If it happens, it happens," one villager told The Guardian.

Misiunas has said the barrier is meant to deter smuggling along the border. It's also a response to Russia's alleged abduction of an Estonian official from a border checkpoint three years ago. Moscow accused the official of spying and smuggling, but many suspect the action was meant to reprove Estonia for its ties to the US and NATO.

The Baltic countries — Estonia, Latvia, Lithuania — have been sounding alarm about Russian action in the region for some time.

A particularly worrying scenario imagined by some is the potential for Russia to close the Suwalki Gap, a 60-mile-long section of the Poland-Lithuania border between Kaliningrad and Belarus. Such a move would cut off the Baltics from the rest of Europe. In June, troops from the US, UK, Poland, Lithuania, and Croatia performed NATO's first large-scale defense exercise in the area.

US Army soldiers leave a Black Hawk helicopter during the Suwalki gap defense exercise in Mikyciai, Lithuania, June 17, 2017. REUTERS/Ints Kalnins

An Estonian intelligence report issued earlier this year reported that Russia's military intelligence agency and Federal Security Service were trying to gather information on and influence the defense planning and military capabilities of its neighbors.

"The Russian intelligence and security services conduct anti-Estonian influence operations, including psychological operations — in other words, influencing the defence forces and the general population of a potential enemy," the report said.

Lithuania expressed concern this spring that Russia was laying the groundwork for "kinetic operations" — meaning military action — through propaganda campaigns. The country's defense minister said there were parallels between what his country was seeing and the annexation of Crimea in 2014.

NATO has deployed troops in the Baltic states and Poland to deter Russia from more land grabs after its 2014 annexation of Crimea. AFP

Lithuania's president has also said she wants a permanent US troop presence in her country "to not only deter but to defend."

NATO has deployed four battalion-size battle groups to the Baltics states as well as Poland already this year.

Russian and NATO aircraft regularly engage each other in the skies over the Baltics and Eastern Europe — at times coming within feet of each other during fly-bys. NATO Secretary General Jens Stoltenberg said earlier this year that the defense bloc was seeing increased Russian military activity "on land, at sea, and in the air."

US European Command said on Wednesday that US fighter aircraft will take over a NATO air-policing mission over the Baltics in September, surveilling the skies there until the end of the year.