Sen. John McCain (R-Ariz.) on Thursday said if the U.S. can confirm that Russian separatists shot down a Malaysian passenger plan, the U.S. should react by imposing tough new sanctions against Russia.

Speaking to reporters, McCain said Russia is the only possible source of surface-to-air missiles that appeared to take down the plane.

Sen. John McCain, R-Ariz., called for tough sanctions against Russia if it can be confirmed Russia aided the separatists who shot down a Malaysian passenger plane. (AP Photo/Susan Walsh)

“The separatists could only have gotten that capability from Russia, and so therefore, the culpable party here is Vladimir Putin,” McCain said.

McCain added that over the last few days, separatists have managed to shoot down a few planes.

“What gives credence to that theory is in the last couple of weeks, the separatists shot down several aircraft, including a transport aircraft that was flying at 21,000 feet,” McCain said. “So they have a record in recent days of shooting down Ukrainian aircraft.”

McCain said Russia has been adding troops and equipment to the Ukraine conflict, and said that demands “stringent” action from the United States. When asked what steps he would recommend, McCain said:

“Arm the Ukrainian military, which shamefully we have not done, increase sanctions to a dramatic degree, label Vladimir Putin and Russia as a pariah nation, which, if they’re responsible for this, they deserve.”