Russian military activity in Syria is now being called a military build-up by U.S. defense officials and is being compared to Russian activity in Crimea last year.
Russia has brought in dozens of armored vehicles and groud support vehicles, in addition to artillery, two defense officials told NBC News. However, officials maintain that the U.S. does not know exactly what Russia is planning in Syria.
The U.S. estimates that Russia may have fewer than 100 military operating in Syria right now. But one defense official said the Russians could have military there in plain clothes unbeknownst to the U.S.