[42] From late 2011[43] and early 2012, Iran's IRGC sent tens of thousands of Iranian troops and Shi'ite foreign paramilitary volunteers in coordination with the Syrian government to prevent the collapse of the regime; thereby polarizing the conflict along sectarian lines.

[55][43] Iranian troops and allied militias on the ground were supported by ballistic missiles and air forces, including armed drones utilizing smart munitions.

[56] At the height of its intervention in 2015–18, an estimated 10,000 IRGC forces and 5,000 Iranian Army members were stationed in Syria alongside tens of thousands of Iranian-led foreign militias.

In 2018, 2,000 officers of the Quds Forces commanded an estimated 131 military garrisons and tens of thousands of Iran-backed Shia jihadists across regime-controlled regions.

[59] Prior to the Syrian war, Iran had between 2,000 and 3,000 IRGC officers stationed in Syria, who helped to train local troops and managing supply routes of arms and money to neighboring Lebanon.

[40] In April 2014, Hossein Amir-Abdollahian, Iranian deputy foreign minister said, "We aren't seeking to have Bashar al-Assad remain president for life.

[60] Using its increased leverage during the civil war, Iranian government had been recruiting Alawites by setting up Khomeinist religious centers to convert them to Twelver Shi'ism.

Iran developed these capabilities in the wake of the 2009 protests and spent millions of dollars establishing a "cyber army" to track down dissidents online.

[41] In May 2012, in an interview with the Iranian Students News Agency which was later removed from its website, the deputy head of Iran's Quds Force said that it had provided combat troops to support Syrian military operations.

The confidential report leaked just hours after an article appeared in The Washington Post revealing how Syrian opposition fighters started to receive more, and better, weapons in an effort paid for by Persian Gulf Arab states and co-ordinated partly by the US.

[71] The alleged spike in Iranian arms was likely a response to a looming influx of weapons and ammunition to the rebels from Gulf states that had been reported shortly before.

[72] On 24 July 2012, Islamic Revolutionary Guards Corp commander Massoud Jazayeri said Iranians would not allow enemy plans to change Syria's political system to succeed.

[73] In August 2012 Leon Panetta accused Iran of setting up a pro-Government militia to fight in Syria, and chairman of the joint chiefs of staff General Martin Dempsey compared it to the Mahdi Army of Iraqi Shia leader Muqtada al-Sadr.

"[79] Iran decided in June 2013 to send 4,000 troops to aid the Syrian government forces, described as a "first contingent" by Robert Fisk of The Independent, who added that the move underscored a Sunni vs. Shiite alignment in the Middle East.

[83] According to American officials questioned by journalist Dexter Filkins, officers from the Quds force have "coordinated attacks, trained militias, and set up an elaborate system to monitor rebel communications" in Syria from late 2012 to 2013.

With help from the Hezbollah, and under the leadership of Quds Force general Qasem Soleimani, the al-Assad government won back strategic territory from rebels in 2013, in particular an important supply route during the Al-Qusayr offensive in April and May.

[86] Iran has stepped up support on the ground for Syrian President Assad, providing hundreds more military specialists to gather intelligence and train troops.

[40][48] This surge of support was in part a decision strongly promoted by Qasem Soleimani, the head of the Quds force, to exploit the outbreak of infighting between rebel fighters and the al-Qaeda inspired Islamic State of Iraq and Sham (ISIS).

[40][48] A Syrian opposition source said in recent months Iranian led forces had begun operating in coastal areas including Tartous and Latakia.

With much of the Syrian Arab Army and National Defence Forces units deployed to more volatile fronts, the Russian Marines and Iranian Revolutionary Guard (IRG) have relieved their positions by installing military checkpoints inside the cities of Slunfeh (east Latakia Governorate), Masyaf (East Tartus Governorate) and Ras al-Bassit (Latakia coastal city).

[112] In January 2019, the Israel Defense Forces confirmed that it had carried out strikes against Iranian military targets in Syria several hours after a rocket was intercepted over the Golan Heights.

[114] On 7 March, an IRGC commander, Farhad Dabirian, was reported to be killed a day earlier in the Sayyidah Zaynab neighborhood in Damascus, without giving details on the circumstances of his death.

[121] Various factions of the Assad regime and many Ba'ath party supporters have also demanded the withdrawal of Hezbollah and other Iran-backed Khomeinist militant groups from Syria.

[123] From January 2013 to March 2017, the Islamic Revolutionary Guard Corps lost 2,100 soldiers in Syria and 7,000 wounded, according to Iran's veterans' affairs office.

[124][125] In August 2017, Brigadier General Hamid Abazari stated that 25% of the soldiers that Iran had sent to Syria had been killed or wounded,[126][127] implying several tens of thousands had served.

"[35] Ali Alfoneh of The Washington Institute for Near East Policy documented a minimum of 559 Iranian combat fatalities as of early 2018[128] based on surveying funeral services in Iran.

[129] Thousands of Iranian-backed Afghan, Lebanese, Iraqi, Yemeni, Pakistani and other militia fighters have also been killed after joining IRGC-sponsored paramilitary organizations.