The Russian government stopped denying they have troops in Syria.

The statement comes one day after the United States asked nations like Bulgaria and Greece to close their airspace to Russian military transports. Bulgaria agreed to the U.S. request but Greece did not publicly respond to the request.

Foreign Ministry spokeswoman Maria Zakharova confirmed “advisors” are assisting with deliveries of Russian arms.  The Russian government is claiming the mission of the forces is just to assist the Syrian army in fighting militants.

However, U.S. officials say that Russian transports are also arriving with passenger flights that contain Russian troops putting together a forward base in Syria.

“Any effort to bolster the Assad regime would potentially be destabilizing,” the U.S. State Department said.

Russia has long considered Syrian President Bashir al-Assad a close ally.