WASHINGTON — (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 not yet operational, 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.”

There are three scenarios where it might be set up in the field in northwestern Syria, a US official said. Two of the locations are considered fairly routine — Bassel Al Assad airport and Masyaf.

However, the third potential location, which is the Baniyas mountain area in northwest Syria, could present more issues for US pilots.

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

If it is set up at a high enough altitude, its radar will be able to “see” over the mountains, allowing Russian air defense coverage to possibly extended as far as the western city of Dier Ezzor, which is a shift in the battlefield, the official said.

Dier Ezzor, which is about 270 miles east of Damascus, sits very close to ISIS-held territory and US and coalition aircraft striking ISIS regularly operate in that area at present.

For months now, the Russians have had air defense that lets them see north to the Turkish border, so this expands the envelope potentially in a militarily significant manner.

US officials feel that Russians likely want to extend their air defense envelope out to Dier Ezzor to demonstrate to the world they and the Syrian regime are in control of wide swath of Syria.

But a US official with direct knowledge of the situation and the thinking inside the administration says the anti-regime forces and other militia forces, the majority of which form the Free Syrian Army, a main anti regime force, are now estimated to total as much as 100,000 fighters across Syria, which means the Syrian military would not likely be able to wipe them out and assert full control on the ground.

The battlefield stalemate appears to have no solution at this point.

The Administration is not considering military options against the Syrian regime, several officials say.

But there are growing signs that inside the Administration there is a rift. Several senior Pentagon officials are making it clear they do not favor military action.

The State Department and the intelligence community are more open about the potential for some type of move to pressure Russia though its not clear what that would be.

On Friday, CIA Director John Brennan told Reuters “I think that pushing back against a bully is appropriate,” adding, “I think that is very different than rushing in and bombing the hell out of a place.”