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Why is Russia increasing its presence in Syria?

While Russian President Vladimir Putin has made no secret of his support for the Assad regime in Syria, the latest movement of Russian forces into the war-torn region is pressuring the United States to take notice.

"[Russia's] supporting Assad against the Islamic State and these jihadi marauders," CBS News senior national security analyst Juan Zarate said. "So they're forcing the U.S. to come to grips with what's happening from a Russian and an Assad perspective."

Last week, Russia set up an air traffic control tower near Syria's Mediterranean port of Latakia -- a sign, Zarate said, that Putin and his administration "want to remain a player there."

"They have an interest in not just the Assad regime, a longtime ally, but their base -- their naval base, which gives them an entrée to the Mediterranean," he told CBS News homeland security correspondent Jeff Pegues.

"They're trying to build leverage as they realize that the United States and the rest of the world is going to try to come to some sort of political accommodation in Syria," Zarate said.

U.S. involvement in a showdown with Russia?

The Obama administration has already said it would not introduce ground troops into the Syrian conflict. Zarate said the proxy forces that the U.S. have attempted to align with -- like the Kurds in the north and some elements of the Free Syrian Army -- have achieved few results.

The U.S. has limits when it comes to Putin, Zarate said.

"The U.S. isn't going away," he said. "The U.S. is going to apply its air power. It's going to continue to supply its forces. If this humanitarian disaster increases, there are going to be calls for a safe zone, which will implicate taking broad swaths of territory sort of off the map militarily. So [Putin's] going to have to contend with a very messy environment."