More than 2,000 militants sent from Iran have been killed in Iraq and Syria, the head of Iran's veterans' affairs office said on Tuesday, France 24 reported.
"Some 2,100 martyrs have been martyred so far in Iraq or other places defending the holy mausoleums," Mohammad Ali Shahidi told the state-run IRNA news agency.
Shahidi, who is head of Iran's Foundation of Martyrs and Veterans Affairs, was speaking at a conference on martyrdom culture in Tehran.
The figure was more than double the number he gave in November, which referred only to Syria.
Iran is, with Russia, the main military backer of Syrian President Bashar al-Assad, and also organises militias fighting the ISIS group in Iraq.
Shahidi did not provide details on the nationalities of those killed.
Iran oversees "volunteer" fighters recruited from among its own nationals as well as Shiite communities in neighbouring Afghanistan and Pakistan.
The families of those killed in battle are given Iranian citizenship under a law passed last May.
Tehran refers to the fighters as "defenders of the shrines" -- a reference to Shiite holy sites in Iraq and Syria that have been targeted by Sunni extremists.