Iran's Revolutionary Guards has recruited thousands of Afghans, some by coercion, to fight in Syria's war alongside forces loyal to President Bashar al-Assad, AFP reports.
"Iran has not just offered Afghan refugees and migrants incentives to fight in Syria, but several said they were threatened with deportation back to Afghanistan unless they did," said Peter Bouckaert, emergencies director at the New York-based Human Rights Watch.
"Faced with this bleak choice, some of these Afghan men and boys fled Iran for Europe."
Shiite Iran is a staunch supporter of Assad and provides financial and military support to his regime.
Tehran says its Fatemiyoun Brigade, comprised of Afghan recruits, are volunteers to defend sacred Shiite sites in Syria and Iraq against Sunni extremists like those of ISIS.
But some reports say the Afghans have been offered residency and a monthly salary to fight for Iran.
The Islamic republic denies having any boots on the ground and insists its commanders and generals act as "military advisers" in Syria and Iraq.