Under Russian laws that have been used broadly 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 its advisor, Laurent Vinatier.

"We are aware that Laurent Vinatier, an advisor at the Centre for Humanitarian Dialogue, has been detained in Russia. We are working to get more details of the circumstances and to secure Laurent's release," it said in a statement.

According to its website, the 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.

Russia's Investigative Committee, which probes major crimes, said Thursday 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.

It said the suspect, which it did not formally name, had "repeatedly visited Russia, including Moscow, where he held meetings with Russian citizens."

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 which carries a maximum prison sentence of five years, if convicted.

It published a video showing a man being approached by officers in a restaurant terrace before being led into a police van.

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.

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