It has been reported that one hundred thousand Afghans have been deported from Iran since late April.
The UN refugee agency in Afghanistan says Iran expelled the Afghans in a drive to deport those who are in the country illegally.
Tehran says it wants one million Afghans repatriated by next March, most of them single men who have been in Iran for a short period.
Afghanistan has asked its neighbor to stop the traffic, saying it does not have the capacity to accommodate so many people at once.
The United States has also expressed concern over the burden of returning deportees.