Tehran deploys its troops, as well as Afghan and Pakistani recruits, to back Syrian President Bashar al-Assad in Syria.

More than 1,000 soldiers deployed by Iran to Syria to back government forces in the civil war have been killed, an Iranian official said on Tuesday.

The death toll was a major increase from one reported just four months ago when Iran announced 400 of its soldiers had died on Syria’s battlefields.

Iran has been sending fighters to Syria since the early stages of the more than five-year-old war to support its ally, President Bashar al-Assad, against armed groups trying to topple him.

Although many of the soldiers Iran sends are its own nationals, it is casting its recruitment net wide, training and deploying predominantly Shia-Muslim fighters from neighbouring Afghanistan and Pakistan as well. Afghan citizens represented half the death toll reported in August.

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“Now the number of Iran’s martyrs as defenders of the shrine has exceeded 1,000,” Mohammadali Shahidi Mahallati, head of Iran’s Foundation of Martyrs, which offers financial support to relatives of those killed fighting for Iran, was quoted as saying by Tasnim news agency.

Iran alludes to its fighters in Syria as “defenders of the shrine”, a reference to the Sayeda Zeinab mosque near Damascus, which is where a granddaughter of the Prophet Mohammad is said to be buried, as well as other shrines revered by Shia.

Many Iranians initially opposed involvement in Syria’s war, harbouring little sympathy for Assad. But now they are warming to the mission, believing ISIL’s threat to the existence of their country is best fought outside Iran’s borders.

The Syrian civil war started as a largely unarmed uprising against Assad in March 2011, but quickly escalated into a full-on armed conflict.

The UN estimates more than 400,000 people have been killed, and 11 million Syrians – half the country’s pre-war population – have been displaced from their homes.