A senior French military officer stationed at a NATO base has been indicted and detained on suspicion of spying for Russia, local media and legal sources said on Sunday.
The reports were at least partially confirmed by French Defence Minister Florence Parly.
The French army officer was stationed abroad, a legal source said confirming details from Europe 1 radio. According to the report, the soldier was stationed on a NATO base in Italy and is suspected of espionage on behalf of Russia.
The French government confirmed it was investigating a senior military officer over a "security breach".
"What I can confirm is that a senior officer is facing legal proceedings for a security breach," Parly told Europe 1 radio, CNews and Les Echos newspaper.
She added that the French authorities had taken "all necessary protective measures" to ensure that the justice system can now do its job without compromising state secret.
She gave no further details.
The French armed forces ministry said it had offered its "full cooperation" on the matter to the judicial authorities.
The legal source said the officer had been indicted and taken into custody on charges involving "intelligence with a foreign power that undermines the fundamental interests of the nation".
He is being prosecuted for "delivering information to a foreign power", "collecting information harming the fundamental interests of the nation with a view to delivering them to a foreign power" and "compromising the secrecy of national defence", the source said.
- Sensitive documents -
Europe 1 said the officer was a lieutenant-colonel stationed with NATO in Italy and had been placed under investigation on suspicion of spying for Russia.
He speaks Russian and was seen in Italy with a man identified as an agent of the GRU, the Russian military intelligence service, the report said.
It said he was suspected of having supplied sensitive documents to Russian intelligence.
According to the French security and defence blog "Mamouth", the suspect was based in Naples, which hosts the main NATO site in Italy.
The man was arrested by DGSI intelligence service as he was about to leave for Italy at the end of his holidays in France, and is being held at a prison in Paris, Europe 1 said.
The alarm was raised in French political circles in July and judicial investigation was opened into possible "treason", the judicial source said.
Such spying accusations are rare but not unknown in the French military, with Russia and the former Soviet Union the main beneficiaries.
In July, two former French spies were arrested after being accused of passing classified information to China, highlighting what experts see as Beijing's push to develop its foreign intelligence capabilities.
In 2001, a French officer detached to NATO was found guilty of providing information to Serbia on the Alliance's strikes against the country during the Kosovo war.
The latest case of suspected spying comes as NATO is going through a difficult period, lambasted by US President Donald Trump amid strategic uncertainties caused by American foreign policy.
There are also soaring tensions between NATO members Turkey and Greece.
French President Emmanuel Macron, a strong proponent of a European defence strategy independent of the US, last year declared that NATO was strategically "brain dead".