U.S. military commanders and experts are sounding warnings about the buildup of Russian submarines off American coasts.

The Russian buildup of naval assets is more expansive than just the Black Sea and the Mediterranean, and it includes seas surrounding the United States, sources told Newsweek.

“Nuclear-powered submarines have been deploying off the coast of the United States and into the Mediterranean and elsewhere along Europe periphery,” Russia Maritime Studies Institute (RMSI) Director Michael Peterson told Newsweek, warning the deployments “mirror Soviet style submarine deployments in the Cold War.”

Among the assets off the coasts are nuclear-capable submarines in the Severodvinsk class, which was also has been warned by U.S. Air Force Gen. Glen VanHerck, who runs the Northern Command and NORAD.

“They just moved subs, their first [Severodvinsk submarine] into the Pacific,” VanHerck warned last October. “Another is out in the Mediterranean right now, and another that’s out on its way into the Atlantic. That will be a persistent, proximate threat capable of carrying a significant number of land-attack cruise missiles that can threaten our homeland.”

The latest warnings come as Vladimir Putin’s war in Ukraine has stretched into its second year and the U.S. continues to ramp up  support for Ukraine’s defense efforts. Putin started his “special military operation” in Ukraine in February 2022 with the warning for the West and NATO allies to remain uninvolved. 

Ukraine has been calling for ever more involvement, asking for advanced weaponry, including missile defense systems, munitions, fighter jets and tanks.

Russia’s navy is one of the strongest submarine forces in the world, particularly in its ability to leverage nuclear capability as a deterrent, according to the report.