The two men, Swedish citizens, are accused of passing information to Russia's GRU military intelligence service over a 10-year period and face life imprisonment.
Two Iranian-born brothers were brought to court in Sweden for allegedly spying for Russia and its military intelligence service GRU for nearly a decade, prosecutors said Friday.
One of the men worked for Sweden's domestic intelligence agency.
Authorities identified the two men as Peyman Kia, 42, and Payam Kia, 35.
The brothers were charged with aggravated espionage, while one of them was also indicted for the alleged gross unauthorised handling of secret information. It was not immediately clear which of the two was being charged with the latter.
Both face up to life imprisonment if convicted. A life sentence in Sweden generally means a minimum of 20-25 years in prison.
"It has been a complex investigation concerning a crime that is very difficult to investigate and the suspicion concerns very serious criminality directed against Sweden's intelligence and security system," National Security Unit chief prosecutor Per Lindqvist said.
"The information that has been obtained, transmitted and divulged could, by the fact that if it comes into the hands of a foreign power, result in detriment to Sweden's security," Lindqvist said in a statement.
Crimes 'very serious', prosecutor says
According to the charge sheet, the men have "jointly" passed information to GRU during the period between 28 September 2011 and 20 September 2021.
It added that the data were acquired through one of the men's work within Sweden's domestic intelligence agency and the country's armed forces.
The data originates from several authorities within the Swedish security and intelligence services.
His brother helped with the contacts with "Russia and the GRU including matters of surrender of information and receipt of compensation."
According to the charges, Payam Kia "dismantled and broke a hard drive which was later found in a trash can" when his brother was arrested.
The case has been investigated by Sweden's domestic security service, SAPO. Sweden's prosecution authority said much of the information in the preliminary investigation is secret and could not offer details.
SAPO said it became suspicious of the former employee, and a preliminary investigation was launched in 2017.
Lindqvist said the inquiry was started "because there was a suspicion that there was a mole, an insider" within Sweden's intelligence community.
The domestic spy agency confirmed that Peyman Kia had worked there between 2014 and 2015, and that before that had worked in the Swedish armed forces.
"It is during these employments that the suspected acquisition must have taken place," Lindqvist said.
Swedish media said that he worked for the armed forces' foreign defence intelligence agency MUST and reportedly worked with a top-secret unit under it dealing with Swedish spies abroad. He later worked for Swedish Customs.
"The suspected crime is a risk that every security service is well aware of, although we do everything to counter it," said Anders Kassman at SAPO.
Peder Ohlsson, head of the armed forces' press department, called the crimes "very serious".
Swedish Defense Minister Pål Jonson said he had been informed of the case but declined to comment.
The brothers became Swedish citizens in 1994. The younger brother reportedly worked for SAPO, Swedish media reported.
They were arrested in September and November 2021. Both have denied any wrongdoing, Swedish media reported.