KEY POINTS
  • The U.S. has it make it clear to Russian President Vladimir Putin that there are lines that the U.S. will not allow Russia to cross, says Leon Panetta.
  • "There are an awful lot of steps that the Russians are taking to be very aggressive," he says.
  • He believes that's due in part to the fact Russia has read weakness into the United States.

The United States has to make it clear to Russian President Vladimir Putin that there are lines that the U.S. will not allow Russia to cross, former Defense Secretary Leon Panetta told CNBC on Tuesday.

"There's no question we're in a new chapter of the Cold War with Russia," Panetta said on "Closing Bell."