French authorities have detained three individuals on suspicion of espionage for Russia and for promoting its war propaganda, prosecutors announced on Tuesday.

These arrests are part of an investigation into the French-Russian group SOS Donbass, amid growing concerns over potential Russian interference throughout Europe due to escalating tensions surrounding Moscow’s invasion of Ukraine.

One of the suspects, a 40-year-old Russian man, was recorded by surveillance cameras in September while putting up pro-Russian posters on the Arc de Triomphe in Paris, according to the city prosecutors’ office.

Following this, he made a phone call to the leader of SOS Donbass, a 40-year-old woman suspected by French counter-intelligence of attempting to gather financial data from French business leaders.

This woman, originally from Russia, had already attracted the attention of France’s domestic intelligence agency, the General Directorate for Internal Security (DGSI), since at least the start of the year.

After the DGSI identified “activities likely to threaten the essential interests of the nation” involving her, a judicial investigator was appointed in March to look into various alleged offenses, including “collusion with a foreign power,” which carries a potential sentence of 10 years in prison.

SOS Donbass claims to be a humanitarian organization providing assistance to civilians in the eastern Donbas area of Ukraine, which is partially controlled by Moscow.

The third individual in custody is a 63-year-old man from the Seine-Saint-Denis region, located in northern Paris.

A fourth suspect, aged 58, has avoided pre-trial detention but is under strict monitoring and must report to the police once a week.