Nuclear weapons are not something that should be the subject of loose rhetoric by world leadership," Carter said. "We all understand the gravity of nuclear dangers. We all understand that Russia is a long established nuclear power. There is no need for Vladimir Putin to make that point."
Carter's comments are just the latest in an escalating war of words between U.S. and Russian officials.
Speaking at the St. Petersburg International Economic Forum on Friday, Putin denied his government is behaving aggressively.
"We are not aggressive," Putin said. "We are persistent in pursuing our interests.