As many as 2,000 Iranian and Iranian-backed forces are currently in Syria helping regime troops in an offensive near Aleppo that is being coordinated with Russia, a US official said Friday.

"There could be as many as 2,000 Iranian-enabled forces" southeast of Aleppo, the official said, speaking on condition of anonymity. He defined those forces as consisting of Iranians, Iranian-funded proxies and Lebanese Hezbollah.

"We are now seeing a coordinated effort between Iran and Russia to assist (President Bashar al-) Assad with fighting opposition groups," the official added.