Russian President Vladimir Putin is deploying nuclear-armed submarines "dangerously close" to the United States and European allies, a Senate Democrat said following a trip to the Arctic Circle.

"No one is suggesting that Putin is contemplating a nuclear launch against a NATO country, but it's not clear how tethered to reality Putin is," Connecticut Sen. Chris Murphy told reporters Monday. "And it should make us nervous that many of his submarines are starting to get dangerously close to the U.S. and our allies."

Murphy made the comments while arguing that the U.S. Navy needs to pursue an aggressive plan to replace aging submarines, which can thwart rival countries from gathering intelligence and maintain the security of global shipping lanes.

In recent years, Putin's navy has pursued a more aggressive strategy than even during the Cold War, Murphy said. "Russian submarines have been pushing out to the very precipice of NATO-ally waters," he said. "We have seen Russian boats coming closer to the U.S. and to our European partner ports than ever before, in immensely provocative ways — in ways that were rare even during the days of the Cold War."

Pentagon officials plan to scale back production of modern attack submarines if the Navy can't get funding to replace Ohio-class ballistic missile submarines. "You're going have to look at this program with a national lens because if you drop this into the middle of a Navy shipbuilding budget it will just gut Navy shipbuilding for decades to come," Navy Secretary Ray Mabus told a House panel last week.

Murphy wants the Navy to build those Ohio-class replacements without cutting production of Virginia-class attack submarines. "We've got to find a way to do both," he said. "If you look at the pace of Russian and Chinese building programs, we can't afford to drop Virginia-class production back to one for more than a year."