A force of hundreds of Iran’s Revolutionary Guards have been deployed in Syria in order to aid Syrian President Bashar Assad’s regime, an Israeli defense source said on Thursday.

The Iranian combat troops have arrived in Syria over the past few days, mostly to aid Hezbollah in their fighting in the Zabadani region in southwest Syria near the border with Lebanon and not far from Damascus.

The Israeli defense establishment says Assad now controls only about a quarter of the territory of Syria, mostly in the area known as “Little Syria,” or “Allawistan,” the Alawite enclaves near Latakia, the port of Tartus and the coastal region in the area. The Syrian capital of Damascus is also under threat, both by the Islamic State (also known as ISIS and ISIL) as well as by other rebel forces.

The last positions on the Golan Heights controlled by Syrian government forces, in the area of the Druze village of Khader and Khan Arnaba, are under pressure from the rebels, who are expanding their control in the region, said the Israeli defense source. This now threatens the last remaining enclave of the Assad regime along the border with Israel on the Golan Heights, he said.

Israel assumes the deployment of the Iranian Revolutionary Guards was done in full coordination between Iran and Russia, and may even have been decided upon at the meeting between the commander of the Revolutionary Guards Quds force Qassem Soleimani and Russian President Vladimir Putin last month in Moscow — a meeting Russia denies took place.

Open gallery view A handout photo released by the official Syrian Arab News Agency shows Syrian President Bashar Assad (R) meeting with Iranian Minister of Economy and Finance Ali Tayebnia, Damascus, March 16, 2015. Credit: AFP PHOTO / HO / SANA

In addition to the Iranian Guards force, which was reported for the first time now by Israeli sources, there are also Russian military forces operating in Syria.

The Kremlin confirmed on Wednesday the reports of Russian soldiers in Syria, though Syria’s information minister denied reports of a Russian military buildup in his country on Tuesday, saying there were no Russian combat forces fighting alongside the army against mainly Islamist insurgents.

Russia’s Foreign Ministry acknowledged on Wednesday that Russian military experts were present in Syria, the first official confirmation that the Russian military is in Syria after weeks of speculation concerning Moscow's growing presence there. Maria Zakharova, a spokeswoman for Russia's Foreign Ministry, said the experts were assisting with Russian arms deliveries to Syria, which Moscow says are aimed at combating terrorism.

Israeli military sources say that at this stage the Russian military presence is mostly limited to advisors, alongside a security force, but that these forces are preparing to deploy Russian fighter planes or combat helicopters with the intention of operating a military airfield near Latakia in the future.

While Moscow claims it is helping the Syrian government fight Islamic militants, Israeli Defense Minister Moshe Ya’alon says the Russian presence is intended to defend Assad’s regime.

“There is a threat to the enclave in Latakia and Tartus, and it is the Russian interest that has led to their presence there. They want to defend the [Assad] regime and participate in the fighting against ISIS,” said Ya’alon on Thursday in a meeting with Israeli military correspondents.

“Will the Russian presence change the balance in Syria? It is hard for us to see that. It seems it will prolong the fighting, since ISIS will not give in, and in our assessment the fighting and bloodshed will continue, with all the human tragedy that the Syrians are experiencing,” said Ya’alon.