Iran's supreme court has upheld the death sentence handed down to a Swedish Iranian dual national convicted of leading an Arab separatist group accused of attacks including one on a military parade in 2018 that killed 25 people, state media reported on Sunday.

Iran said in 2020 that its security forces arrested Habib Farajollah Chaab abroad, without saying where or how he was captured.

"Chaab was sentenced to death after several court sessions with the presence of his lawyer ... The Supreme Court confirmed the death sentence," Iran's judiciary's Mizan news agency reported.

Chaab was charged with leading the separatist Arab Struggle Movement for the Liberation of Ahwaz, which seeks a separate state in the oil-rich Khuzestan province in southwestern Iran, and plotting and carrying out "numerous bombings and terrorist operations" state media reported when his trial began that same year.

He was also charged with being "corrupt on Earth", a capital offence under Iran’s strict form of Islamic law, Iranian state media said.

Iran has had tense relations with its ethnic minorities, which include Arabs, Kurds, Azeris and Baluch, and has accused them of aligning with neighbouring countries rather than Tehran.

Arabs and other minorities have long said they face discrimination in Iran, a charge the Islamic Republic denies.