REUTERS — On the curbside outside the civilian airport in Kaliningrad, Russia's Baltic Sea outpost, a group of about 20 servicemen in Russian navy uniforms lined up earlier this month, waiting for a bus to take them to their base.

"We are an additional reinforcement," one of the young men, who said he and his colleagues had flown in that day, told Reuters as they waited on the rain-soaked tarmac. He gave no further details.

Russia and NATO are each building up their military capability across eastern Europe, spurred by the conflict in Ukraine which has prompted officials on both sides to talk of the risk of a new, Cold War-style confrontation.

Open gallery view A military base under construction in Pionersky in Kaliningrad region, Russia, June 23, 2016. Credit: Reuters

For Russia, a strategic centerpiece is here in Kaliningrad. A relic of the Soviet Union, it is a small piece of Russian territory sandwiched between NATO members Poland and Lithuania, allowing the Kremlin to project its military power into the alliance's northern flank.

During a three-day visit by Reuters earlier this month, there was ample visible evidence of Russia enhancing its military presence.

Trucks moved military equipment from a port to locations inland, small groups of servicemen flew in, work was under way to boost security near one base and extensive construction was taking place at another base housing a military radar system.

Reuters was able to see only a glimpse of what the Russian military is doing in Kaliningrad. Much of the region is off-limits to foreigners without a special permit and at one point men in civilian clothes ordered photos of military infrastructure deleted. The Russian defense ministry did not respond to questions about its deployments in Kaliningrad.

But much of the activity tallied with what military analysts and Western diplomats say Russia is doing: preparing to station new missiles in Kaliningrad and build a web of anti-aircraft systems that could challenge NATO aircraft over the Baltic states and parts of Poland.

Russia's military build-up will be on the agenda when leaders of NATO member states meet in Warsaw on July 8 for an alliance summit. Russia says it has been forced to respond because NATO is drawing closer to its borders.

"When it comes to threats in the (Kaliningrad) area, indeed we can talk of an increase in the intensity of Russia's aggression in recent days," Poland's Defence Minister Antoni Macierewicz told Reuters.

"These threats have a very important, dangerous role, always present in NATO's thinking – these are anti-access activities, which are a serious threat to the alliance.”

Radar Station

Kaliningrad was born after World War Two when Soviet troops occupied the German port of Koenigsberg.

The war left most of the city bombed to rubble. The remaining German population was expelled and the city annexed to the Soviet Union, resettled with Russians and renamed Kaliningrad in honor of a Soviet leader who died in 1946. After the breakup of the Soviet Union in 1991 it became a Russian exclave, with no land borders with other parts of Russia.

According to NATO planners, Russia is using Kaliningrad to pursue what is known as an anti-access/area denial (A2/AD) strategy for surrounding areas.

That involves a strategic layering of surface-to-air missiles to block off NATO's air access, if needed, to the three Baltic states and about a third of Poland.

Some Western officials believe the Baltic states, which have large ethnic Russian minorities, could be seized by Moscow, much as Russia took control of Ukraine's Crimea region two years ago. Moscow says it has no such intention, but needs to beef up its defenses because of NATO buildup in the Baltic.

Unlike Ukraine, the Baltic states are part of NATO, which means the alliance would be bound to act to protect them from any threat to their territory.

A European Union diplomat who focuses on security said Russia's strategy for adding anti-air capability in Kaliningrad "will only progress -- the process is centralized and well-coordinated."

"And the Russians spend the greatest amount of financial resources on those capabilities," the diplomat said. "The question is what is it intended for?"

The biggest construction works seen by Reuters were at the Pionersky Radar Station, on Kaliningrad's northern coast. The radar itself, whose range covers all of Europe and which gives early warning of air attack, became operational in 2014.

Now, the military is expanding the infrastructure around it. Trucks carrying sand and gravel could be seen driving into the base. Dump trucks, a truck-mounted crane and an excavator were parked nearby. Construction workers walked in and out of the base, some in camouflage trousers.

"The station is strategic for Russia, that's where a lot of work is going on," said a soldier based there.

Information posted on the website of Russia's Federal Agency for Special Construction, which carries out construction projects for the military, said work was underway to build barracks, a heating plant, canteens, a medical station, storage units, a firefighting station, a social club and sports facilities.

New buildings could be seen behind the gate into the base. Two local sources said the new accommodation could house up to several hundred service personnel.

Military activity could also be observed in the region's main city, also called Kaliningrad. Military trucks could be seen emerging from the Kaliningrad port - a civilian facility that has a military section - and heading to other parts of the region.

Several of the trucks were carrying small artillery pieces. Others had containers on the back, and in other cases the cargo was concealed beneath a tarpaulin.

At a third location, near the town of Svetlyi, a watchtower just off the road had been renovated, and a swathe of forest around it had been freshly felled to improve sight lines from the tower.

Two local sources familiar with the military set-up in the region said the watchtower was part of a chain of security to protect a military compound near Svetlyi that stored the arsenal of Russia's Baltic Fleet, headquartered at the nearby port of Baltiysk.

Missile Preparations

Russia is likely to deploy the Iskander-M ballistic missiles in Kaliningrad within the next two to three years, sources close to its military have told Reuters.

That deployment is part of a long-standing plan to modernize Russia's non-nuclear ballistic missile system, but Russia is likely to cast it as its response to NATO's own build-up.

In Kaliningrad, Reuters did not see any evidence of preparations to deploy the missiles.

However, two local sources, one with direct knowledge of the Baltiysk naval base, said that the infrastructure work to house an unspecified number of the Iskander missiles has been completed at the base.

Moscow's plan for Kaliningrad is not to flood it with troops and firepower, but to modernize its military infrastructure, said Vladimir Abramov, a Kaliningrad-based analyst who said he believed the West and Russia were equally to blame for their stand-off.

"The Kaliningrad contingent is being heavily upgraded qualitatively, not quantitatively," said Abramov. "Our general staff understands the folly of a large deployment here."