Kaliningrad -- Russian territory that's sandwiched between Poland and the Baltics but disconnected from the rest of Russia, known as an exclave -- has been a focal point in tensions between Russia and the West.
Now, satellite imagery and analysis from ImageSat International, a commercial satellite firm, appear to confirm that a major modernization is underway in at least four locations throughout the region.
Those upgrades include fresh work at what analysts have identified as the Kaliningrad nuclear weapons storage site. Images captured between July 19 and Oct. 1 indicate work on an exposed bunker under renovation that appears to conceal activity underneath.
Another set of images shows 40 new bunkers under construction, increasing capacity at a military storage area near Primorsk, Russia's second-largest port on the Baltic Sea. The new bunkers surround older, smaller bunkers at the center of the site. Images from July 18 show the bunkers under construction; 10 weeks later, the bunkers appear complete.
A short distance north of Kaliningrad, images appear to show upgrades to the Chkalovsk air base, including a new railway and the installation of an instrument landing system that would allow aircraft to land in inclement weather.
A final set of images shows the upgrades in Chernyakhovsk, a base that houses the 152nd Missile Brigade of the Russian military. In February, the base received nuclear-capable Iskander missiles, prompting a U.S. defense official to call it "the biggest move we've seen" in terms of Russian militarization of the Baltics.
The Russian military did not immediately respond to CNN's request for comment on new evidence of military modernization in Kaliningrad. But the Russian government has consistently defended its right to deploy weapons there.