“Following a very long investigation, the General Directorate of Internal Security (DGSI) revealed on Sunday April 10 a clandestine operation carried out by the Russian intelligence services on our territory,” the ministry said in a statement, without elaborating.

“Six Russian agents operating under diplomatic cover and whose activities proved contrary to our national interests have been declared persona non grata,” it said.

Interior Minister Gerald Darmanin congratulated DGSI staff on Twitter for hindering the operation. He gave no details of the nature of the mission. The foreign ministry also declined to give details.

In the absence of Russia’s ambassador in Paris, his number two had been summoned to inform him of the reasons for the expulsion, the foreign ministry said.

“Russia will respond accordingly,” news agency TASS quoted foreign ministry spokeswoman Maria Zakharova as saying.

France earlier this month expelled 35 Russians with diplomatic status as part of a broader European move and said the agents had been working against France’s interests.

Despite some criticism, President Emmanuel Macron has sought to maintain a dialogue with Russian President Vladimir Putin. He speaks regularly with Putin as part of efforts to achieve a ceasefire in Ukraine and begin a credible negotiation between Kyiv and Moscow.

Tensions, however, have mounted in recent weeks with the Russian ambassador being summoned three times, including twice over tweets by his embassy that France described as unacceptable. Read full story