Russia on Thursday detained a Frenchman working for a Geneva-based conflict mediation NGO, accusing him of gathering military information and failing to register as a "foreign agent", Moscow officials said.
Under Russian laws used to crackdown on Kremlin critics, anybody who receives foreign support or who is under "foreign influence" must register as a "foreign agent".
The Centre for Humanitarian Dialogue told AFP it was trying to secure the release of one member of its team.
"We are aware that Laurent Vinatier, an advisor at the Centre for Humanitarian Dialogue, has been detained in Russia," it said in a statement.
"We are working to get more details of the circumstances and to secure Laurent's release."
A video published by Russia's Investigative Committee, which probes major crimes, showed a man being approached by officers in a restaurant terrace before being led into a police van.
In Paris, the foreign ministry said it was aware of the arrest of the French citizen and said its Moscow embassy had asked for consular protection for him and also more details from the Russian authorities.
According to its website, the Geneva-based centre "works to prevent and resolve armed conflicts around the world through mediation and discreet diplomacy".
Russia has previously used "foreign agent" charges as a pretext to arrest people before levelling more serious charges.
But the law has typically been used to target Russian citizens and domestic critics of the Kremlin, such as activists, campaigners and independent journalists.
The Investigative Committee said Thursday that law enforcement had detained a French citizen "suspected of collecting information on Russia's military activities.
"This information, if obtained by foreign sources, could be used against the security of the state," it added.
The suspect, which it did not formally name, had "repeatedly visited Russia, including Moscow, where he held meetings with Russian citizens", it added.
Vinatier is a researcher, consultant and political analyst whose work focuses on Russia and other post-Soviet states, according to his LinkedIn profile.
The Investigative Committee said he had been charged with failing to submit documents needed for "inclusion in the register of foreign agents" -- a charge that carries up to five years in prison, if convicted.
US-Russian journalist Alsu Kurmasheva was arrested on a similar charge last year, before a more serious case of spreading "false information" about the army was levelled against her.
France's domestic intelligence agency the DGSI has since Monday been holding a 26-year-old Russian-Ukrainian man on suspicion of planning a violent act after he injured himself in an explosion.
The case is being handled by Paris anti-terror prosecutors but it has not been made public what target he is suspected of having planned to attack.
