The Russian military has shipped more advanced anti-aircraft and anti-missile systems into Syria, a U.S. official told CNN.
The new system is a modified version of the S-300VM, which is also known as the SA-23.
While the system is not yet operational and the U.S. doesn't believe Russians plan to target American pilots, one official told CNN the development was "a concern."
U.S. officials said there are three possible places where the new system may be housed. Two of the locations are fairly routine -- the Bassel Al Assad airport and Masyaf.
The third potential location, however, which is the Baniyas mountain area, may be a bit more problematic for U.S. soldiers.
According to CNN, if the system is placed at a high enough altitude, its radar will be able to "see" over the mountains. This poses a problem because that could extend Russian air defense coverage and cause a shift in the battlefield.
U.S. officials said Russia likely wants to extend its air defense coverage as far as the city of Dier Ezzor to show they, along with the Syrian regime, are in control of a large portion of Syria.
But an official with knowledge of the situation told CNN that is not the case.
That official said there are an estimated 100,000 anti-regime forces and other militia across Syria, which means it is unlikely the Syrian military would be able to gain full control on the ground.
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