Iran has sent hundreds of troops to Syria in its first open deployment of forces to the civil war-torn country. Iranian forces are joining fighters from the Iranian ally and Lebanese terror group Hezbollah in a likely battle against Syrian rebels and in favor of the regime of President Bashar al-Assad. The forces are benefiting from cover due to Russia’s airstrikes on the country.

A Syrian official and activist who spoke on condition of anonymity reported that about 1,500 Iranian fighters began arriving in Syria about two weeks ago when the Russian airstrikes began, and more are arriving in recent days. Additional Hezbollah fighters have also been arriving. The Syrian Observatory for Human Rights confirmed on Wednesday that Iranian troops are arriving in Syria.

Russia claims that it is trying to stop the Islamic State terror group in Syria, but this is being disputed by Syrian rebels and Western officials, who say the airstrikes are taking place in parts of the country where the Islamic State has little presence. The arrival of additional Iranian and Hezbollah fighters seems to show that Russia’s main goal is to protect Assad’s regime.

“Sending more troops from Hezbollah, and Iran only increases the shelf life of the Syrian regime, which is destined to end,” said Maj. Jamil Saleh, the leader of the CIA-backed Free Syrian Army faction Tajammu Alezzah, according to the Associated Press. “It will only add more destruction and displacement.”