Iranian security and intelligence services have abducted Habib Asyud, the former head of the Arab Struggle Movement for the Liberation of Ahwaz, the head of the Iranian Parliament's National Security Committee said on Sunday.
Mojtaba Dhu Al Nuri said Mr Asyud is currently under investigation in Tehran after being taken from Turkey.
The Arab Struggle Movement for the Liberation of Ahwaz is a separatist group based in the oil-rich south-west of Iran. It is classified as a terrorist group by Iran.
"The arrest of the leader of an Ahwazi group and his transfer to Tehran is another great success for the intelligence and security services in our country," Mr Dhu Al Nuri told the Iranian Parliament News Agency.
"The accused will receive his punishment in a trial after taking the necessary information from him in the investigation and completion of the case," he added.
The Swedish Ministry of Foreign Affairs told Swedish TV it was aware of his arrest in Turkey and his extradition to Iran.
His wife, Hoda Hawashmi said her husband boarded a flight to Turkey, intending to travel on to Doha. While in transit in the country, Ankara handed him over to Iranian intelligence, she said.
Mr Asyud, 47, holds Swedish citizenship and could face the death penalty, according to Tehran. The arrest risks embroiling Sweden in a diplomatic tussle over Mr Asyud's life.
The Iranian armed forces news agency said on Friday that Turkish authorities had handed Mr Asyud to Iran. The transfer took place through the port of West Azerbaijan province, in north-west Iran, it said.
It is expected that Turkey's extradition of a Swedish citizen to Iran will have a negative impact on Ankara's recently strained relationship with the European Union.
ASMLA said Mr Asyud was kidnapped “after a process of enticement in which a Gulf Arab country participated and contributed”, without naming it. But Ahwazi activists on Twitter accused Qatar of complicity in luring and kidnapping the former head of the movement.
In a statement, the movement said Iran had pursued “a policy of assassinations or kidnapping and detention, to exclude members of the movement from their role in the fields of political and media work”.