A French political expert must remain in custody until August 5 following his arrest in Moscow, the judge in charge decided on Friday, according to Russia's TASS news agency.
According to the Russian judiciary, the employee of a Swiss non-governmental organization (NGO) is alleged to have collected information on military and defence technology in Russia.
However, he was not accused of espionage; instead authorities said that he had failed to register as a so-called foreign agent when collecting information for years.
The man admitted this accusation in court, TASS reported.
According to Russia's law on so-called foreign agents, organizations and individuals that are fully or partially financed from abroad must register. In the increasingly repressive atmosphere in Russia, the law is used to brand critics and restrict their contacts in the country.
Under the criminal legislation, the man's actions are punishable by up to five years in prison or forced labour.
The Swiss organization for which the Frenchman works is reportedly involved in international conflict resolution and quiet diplomacy.
The case can therefore be interpreted against the backdrop of Russia's invasion of Ukraine. Switzerland is organizing a major international peace conference for Ukraine near Lucerne next week - a meeting to which Russia has not been invited and which it fiercely opposes.
At the same time, relations between Moscow and Paris are tense because French President Emmanuel Macron is trying to organize European resistance to Russia's war against Ukraine.
By arresting foreigners, Russia is exerting pressure on other states and using these individuals as bargaining chips for possible exchange deals.