NATO advance force battalion group (EFP) demonstrates a water obstacle crossing during an International exercise "Iron Wolf 2017 /Saber Strike 2017
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(CNN) —  

Russia may have significantly modernized a nuclear weapons storage bunker in Kaliningrad, a sensitive exclave of Russian territory sandwiched between Poland and the Baltics, as tensions between Russia and the West continue to rise, according to a new report.

On Monday, the Federation of American Scientists (FAS) published aerial photographs that the group says show the facility in the Baltic outpost has been under major renovation since 2016.

FAS said the images document refurbishments at the site back in 2016, when one of three underground bunkers at the location was excavated and deepened before it appeared to have been covered over in recent months, “presumably to return (to) operational status soon.”

A satellite image from the Federation of American Scientists that apparently shows a buried nuclear weapons storage bunker in the Kaliningrad region, which the group says has been under major renovation since mid-2016.
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Hans M. Kristensen, the director of the nuclear information project at FAS, said in a blog post that it was unclear from the images if any nuclear weapons had ever been or will be kept at the facility.

“The features of the site suggest it could potentially serve Russian Air Force or Navy dual-capable forces. But it could also be a joint site, potentially servicing nuclear warheads for both Air Force, Navy, Army, air-defense, and coastal defense forces in the region,” Kristensen wrote.

“It is to my knowledge the only nuclear weapons storage site in the Kaliningrad region,” he continued.

Russian foothold in Europe

Kaliningrad is an isolated pocket of sovereign Russia on the Baltic coast where several soccer games will be played during the 2018 World Cup.

The Kremlin has not yet commented on reports of any modernization occurring at the site in Kaliningrad but has previously defended its right to deploy weapons there.

Kristensen said that Russia maintained that nuclear warheads are kept in “central” storage believed to be inside mainland Russia. He proposed that the facility in Kaliningrad “could potentially function as a forward storage site that would be supplied with warheads from central storage sites in a crisis.”

Tensions in Eastern Europe have been building since Russia’s annexation of Crimea from Ukraine in 2014.

In February, US and European officials expressed concern over Russia’s militarization of the Baltics after the Kremlin deployed new Iskander missiles to Kaliningrad. A US defense official based in Europe characterized the positioning of missiles at the time as “the biggest move we’ve seen.”

A month later, Russian President Vladimir Putin unveiled a new “invincible” missile that he claimed would render NATO defenses “completely useless.” In an annual address to the Russian parliament, the Duma, the Kremlin leader said Moscow’s new arsenal had been developed in response to moves in Washington.