The men had been found guilty of promoting terror in Iran and passing on information for Saudi intelligence services.
Three members of an Iranian separatist group have been given prison sentences in Denmark for spying for Saudi Arabia.
The men -- aged between 40 and 51 -- were found guilty of terror charges and passing on information for Saudi intelligence services between 2012 and 2020.
Habib Yabor Kabi -- the leader of the opposition group -- was sentenced to eight years in prison and his brother, Tamim Farouk Beck, to seven years.
Kabi's son-in-law, Jacob Mohamed, was sentenced to six years in prison but was not stripped of his Danish nationality.
Last month, all three were convicted of "promoting terrorism" by supporting the activities of the armed wing of the Arab Movement for the Liberation of Ahvaz (ASMLA).
Prosecutors said that the men had gathered information about dozens of individuals and organisations -- both in Denmark and abroad -- as well as on Iranian military affairs, in exchange for up to 15 million kroner (€2 million). They had all denied the charges.
Two of the suspects will also be deported once their prison sentence is finished, the court in Roskilde said.
The men were arrested in February 2020 while living in exile in Ringsted, 60 kilometres southwest of the Danish capital, Copenhagen.
Denmark’s Security and Intelligence Service say they started an investigation into the case in November 2018.
Ironically, police identified the suspects when one of the three men was the target of an alleged Iranian assassination plot on Danish soil.
The trial in Denmark has ongoing tensions within Europe, where Iran has regularly accused Saudi Arabia of supporting overseas separatist groups.