The Kremlin is modernizing and repairing approximately 20 warships and submarines as part of the country’s rearmament program, Russian government backed media outlet Sputnik reported Monday. The move comes as the U.S. announced it was increasing its defense budget in Europe to counter Russian aggression.

“At the moment, some 20 warships and submarines of various series, including the missile cruiser Marshal Ustinov, the heavy nuclear-powered missile cruiser Admiral Nakhimov, the large anti-submarine warfare ships the Admiral Chabanenko and the Admiral Tributs, the guard ship Neustrashimy, the large amphibious landing ships the Kaliningrad and the Oslyabya, are being repaired and modernized,” a source told Russian media outlet RIA Novosti.

The source added that two nuclear missile cruisers would be updated in the next five years. The Russian military upgrades are part of the country’s rearmament program that began in 2010.

The announcement comes as NATO has reported seeing submarine activity in the North Atlantic region back at Cold War levels, creating “concern” for the military and political alliance, IHS Jane’s, a defense analysis group, reported. NATO Vice Admiral Clive Johnstone said Russian submarines were exhibiting new technical capabilities “that we haven't seen before.” He described Russian submarines as now having longer ranges and better systems.

“I think none of that would worry us if we knew what the game plans were or we knew why they were deploying or what they were doing … we don't understand what the strategic and operational objectives are of the Russian state,” Johnstone said.

Concerns over Russia’s aggression in Eastern Europe following the annexation of Crimea in March 2014 from Ukraine and the ongoing conflict in the Donbass region that has left over 9,000 dead have prompted the U.S. to refocus its defense budget on Europe. Secretary of Defense Ashton Carter said this month that $3.4 billion would be requested in the 2017 budget to aid the European Reassurance Initiative with a focus on Russian threats.