A former member of the Swedish intelligence service could be sentenced to life in jail if found guilty of spying for Russia, according to prosecutors.
Iran-born Peyman Kia, 42, and his brother Payam, 35, are facing accusations they worked together to pass information to Russia between September 28, 2011, and September 20, 2021.
Their trial, which opened in late November, is mainly being held behind closed doors given the "extremely sensitive material" allegedly divulged by the pair.
Peyman, who worked for Sweden's intelligence service Sapo and intelligence units in the Swedish army between 2014 and 2015, could face life in jail if found guilty of "aggravated espionage" for Russia's GRU military intelligence service between 2011 and 2021.
The prosecution is seeking at least 12 years jail for Payam Kia, accused of involvement in planning espionage as well as "managing contacts with Russia and the GRU, including the transfer and collection" of financial transactions.
The brothers are naturalised Swedish citizens, according to media reports.
Both men have denied the charges and their defence counsel has urged they be acquitted, according to Swedish news agency TT.
The prosecutors have requested that much of the material in the case be classified even after the end of the trial, due to its sensitive nature
The trial of the pair coincides with another spectacular spying case believed to have benefited Russia involving a couple of Russian origin arrested late last month at a villa just outside Stockholm in a dawn police helicopter raid.
Moscow allegedly installed the couple, named by the Bellingcat investigative website as Sergei Skvortsov and Elena Koulkova, as sleeper agents in the late 1990s.
According to Swedish media, the pair managed specialist import-export companies dealing in electronic components and industrial technology.
Skvortsov was placed in temporary custody late last month for "illegal intelligence activities" while his companion was detained on suspicion of complicity before being released although she remains a person of interest in the investigation.
Swedish authorities say the case is not linked to that of the Kia brothers.