An official at Iran's Interior Ministry says the estimated 1.5 million Afghan refugees illegally living in the country could face arrest and detention for up to five years.
He says Iranian officials now have legal authority to begin moving unregistered refugees into detention camps with prison-like conditions.
Iran began expelling tens of thousands of Afghan immigrants last April by loading them on buses and dropping them off at the Iran-Afghanistan border.
Several million Afghans fled to Iran after the Soviet invasion of Afghanistan almost 30 years ago and from subsequent fighting among Afghan factions. Iranian officials say the immigrants are causing a strain on the economy.
Since 2002, the United Nations Refugee Agency has helped 800,000 Afghans in Iran return home. But in recent years the number of returnees has declined because of increasing violence in Afghanistan.
Some information for this report was provided by AFP.