French Defense Minister Florence Parly told French media on Sunday that a senior military officer was under investigation for "serious security breaches."
"What I can confirm is that a senior officer is facing legal proceedings for a security breach," Parly told Europe 1 radio. She made similar statements to French television network Cnews and Les Echos newspaper.
The lieutenant-colonel was reportedly based at a NATO facility in Italy and was arrested while holidaying in his native France. He had reportedly passed on "ultra-sensitive" information to Russian intelligence services.
Parly said France's armed forces have taken "necessary protective measures" following the security breach.
The arrest comes a week after US authorities arrested a former Special Forces officer for sharing his unit's activities with Russian intelligence.
According to prosecutors, the Green Beret serviceman, who had been stationed in Germany and Azerbaijan, "thought that the United States was too dominant in the world and needed to be cut down to size."
The NATO alliance has been on alert since 2014, when Russia fomented unrest and annexed parts of Ukraine following an internationally-condemned referendum. Western officials have also accused Russia of undermining global security by engaging in hybrid warfare.
Read more: Germany calls for EU sanctions against Russia
In June, German Chancellor Angela Merkel said a cyberattack on the Bundestag that resulted in sensitive information being siphoned off the network was part of Russia's "strategy of hybrid warfare including cyber disorientation and fact manipulation."
ls/dj (AFP, AP)