A Russian court on Monday sentenced a French researcher to three years in a penal colony after finding him guilty of breaching a "foreign agent" law.

The trial of Laurent Vinatier, who works for a Swiss conflict mediation NGO, comes amid tensions between Russia and the West over the Ukraine war.

The 48-year-old was arrested in Moscow in June and charged with gathering information on Russia's military without being registered as a "foreign agent".

Judge Natalya Cheprasova at Moscow's Zamoskvoretsky district court ruled that Vinatier was guilty and sentenced him to three years in a penal colony, two years less than the maximum possible sentence.

His lawyer Pavel Mamonov told journalists: "We consider the sentence harsh and will definitely appeal."

The Frenchman had acknowledged violating Russian law, saying he was unaware he should have registered as a "foreign agent".

The prosecutor had requested a sentence of three years and three months, saying Vinatier "repented" but the case involved "significant threats connected to Russia's security".

Another lawyer for Vinatier, Oleg Bessonov, had asked the judge to issue him with a fine.

French President Emmanuel Macron had demanded Vinatier's release, saying the "propaganda" against him "does not match reality".

Vinatier was charged over a requirement introduced in 2022 that people who gather information on Russia's military and arms that could harm the country's national security, must register as "foreign agents".

Tensions between Moscow and Paris are running high after France charged Russian-born Telegram founder Pavel Durov in August over illegal content on the popular social media platform, with the Kremlin warning against "political persecution". (AFP)