Story highlights A new missile defense system significantly expands Russia's anti-air capability in northwest Syria

If it is set up at a high enough altitude, the radar will be able to "see" over nearby mountains

(CNN) The Russian military has brought an additional, more advanced anti-aircraft and anti-missile system into Syria, a US official told CNN on Tuesday.

While fully in place but not yet activated, the system, which was shipped in over the weekend, is a newer, modified version of the S-300VM, also known as the SA-23.

It expands Russia's anti-air capability in northwest Syria significantly. Though the US does not believe the Russians plan to target US pilots, one official called the development "a concern."

The system is a newer version of the S-300VM (pictured).

The system is located in a mountainous area that the US believes gives the Russians significant extended air coverage. The radar extends into Turkey and eastern Syria when it's placed on a mountain.

Fox News first reported the missile system being brought into Syria.

Read More