A group of over a dozen Russian spies belonging to an elite unit of military intelligence that carried out operations in Europe including the attempted poisoning of defector Sergei Skripal used a French alpine region as a rear base, a report said on Wednesday.

The Le Monde daily said an investigation by British, Swiss, French, and US intelligence had drawn up a list of 15 members of the 29155 unit of Russia’s GRU military spy agency who moved within Europe from 2014-2018.

It said they had all at some point passed through France’s southeastern alpine region of the Haute-Savoie close to the Swiss and Italian borders, including notably the towns of Chamonix, Evian and Annemasse.

Le Monde published a list of 15 Russian members of the unit, which it said added five more names to those already published by online investigative outlets such as Bellingcat and The Insider. It said that the Western intelligence services began the investigation retrospectively after the attempted poisoning of Skripal in the English town of Salisbury in March 2018.

Britain and its allies accuse the Kremlin of seeking to assassinate Skripal, a charge vehemently denied by Russia. The unit was also active in areas such as Bulgaria, Moldova, and Montenegro.

The paper said some agents came to France repeatedly, others just once or twice. One possibility is that by staying in the French region, the agents hoped to shake off any suspicion before they carried out their missions. Those who stayed in the Haute-Savoie included Alexander Petrov and Ruslan Boshirov – the cover names of the two GRU agents accused of carrying out the attack on Skripal.

The Western intelligence services have not so far found any material, including arms, left behind by the agents during their stays in France, Le Monde said. But their presence has been confirmed by where they ate, stayed and also shopped in the Haute-Savoie, it said. “The most likely hypothesis is to consider it (Haute-Savoie) as a rear base for all the clandestine operations carried out by unit 29155 in Europe,” said a senior French intelligence official, quoted by Le Monde.

The story came as Germany expelled two Russian diplomats after prosecutors said Moscow could be behind the killing of a former Chechen rebel commander in a Berlin park.