Sinisalu noted that a criminal investigation was launched under the paragraph of the Penal Code addressing engagement by an alien in non-violent activities directed against the independence and sovereignty or territorial integrity of the Republic of Estonia.

As the investigation is ongoing, more detailed information cannot yet be provided about the case. "When the time is right, the Office of the Prosecutor General and the ISS will surely provide information to the extent possible," confirmed the director general.

The Russian citizen arrested on Jan. 9 faces up to 15 years in prison if found guilty.

Similar recent cases resulted in conviction

Inna Ombler, the state prosecutor leading the criminal investigation, told ERR that the suspect remains in custody with the permission of the courts.

"The Prosecutor's Office has always valued its cooperation with the ISS," said Ombler. "Over the past two years, we have taken a total of five crimes against the state to court. These cases by now have criminal convictions which have entered into force."

According to the state prosecutor, particularly evident in recent years has been the interest of Russian special services in Estonian citizens who do not specifically have access to state secrets.

"As a rule, these are individuals who are citizens of of the Republic of Estonia or the Russian Federation who are involved in committing various cross-border crimes, which facilitates their recruitment by Russian special services for collusion against the Estonian state," Ombler explained.