The commander of the Afghan Fatemiyoun Brigade was among the dead
Iran was to hold a memorial service on Tuesday for seven Afghans killed fighting alongside the forces of its close ally Syrian President Bashar al-Assad, Iranian media reported.
Among the dead was the commander of Afghan volunteer unit the Fatemiyoun Brigade, the government daily Iran reported.
Alireza Tavassoli was killed in Daraa province, south of Damascus, on February 28 during heavy fighting with Syria's Al-Qaeda branch Al-Nusra Front, the Rajanews.com website reported.
It said all seven of the dead being commemorated in Iran's second city Mashhad were Afghan volunteers.
The Wall Street Journal reported last May that Iran was recruiting Afghan refugees to fight in Syria, in exchange for $500 a month and residency permits.
Iran's foreign ministry spokeswoman Marzieh Afkham at the time dismissed the report as an "insult to the people of Afghanistan."
Iranian media have reported many Iranian deaths in the conflicts in Iraq and Syria.
But the authorities insist nearly all were volunteers who had gone to help guard the Shiite holy places in the two countries against "extremists".
The Iranian government acknowledges that it has a small number of military advisers in both Iraq and Syria but denies having any combat troops on the ground.
Brigadier General Hamid Taghavi was killed in the Iraqi shrine city of Samarra in December while advising Iraqi troops on the war against IS.
European killed fighting IS in Syria
Meanwhile, a foreign fighter believed to be either British or Greek has been killed in Syria while battling the IS alongside Kurdish militia, the Syrian Observatory for Human Rights said Tuesday.
The Observatory said the man died early Tuesday from wounds suffered in a battle with militants the day before in the northeastern province of Hasakeh.
Observatory director Rami Abdel Rahman told AFP the fighter was "a European citizen who had been living in Britain, but it is not clear whether he was British or Greek."
He had been fighting with the Kurdish People's Protection Units (YPG), a local militia, in an area southwest of the town of Tal Hamis, which Kurdish fighters seized from IS last week.
He was the second Westerner believed to have died fighting with the Kurds against IS, after an Australian was reported killed in the same area last week.
Dozens of Westerners are believed to have joined the ranks of the YPG in Syria and other militia battling IS, including Assyrian Christian forces in Iraq.