The Pentagon says increased Russian flights over parts of Europe are unhelpful to the security situation there and risks an escalation of tensions.
NATO has been tracking Russian fighter jets, long-range bombers and tankers across the Baltics, North Sea, and Atlantic Ocean.
Pentagon spokesman Rear Admiral John Kirby said Friday the flights could also pose a risk to civilian aviation because of their number, size and scope.
Kirby also said Russia's continued interference inside Ukraine is unhelpful. He said Russia must try to do the right thing, meet its international obligations and take concrete steps to reduce tensions.
Tensions between NATO and Moscow have escalated since Russia annexed the Crimean Peninsula from Ukraine in March. NATO also accuses Moscow of supporting pro-Russian separatists in eastern Ukraine. Russian President Vladimir Putin has blamed the West for the Ukraine crisis, which he said was being used to "resuscitate" NATO.