Two Russian diplomats that Germany expelled over the assassination of a Chechen rebel in Berlin worked for the GRU military intelligence agency, Germany’s Süddeutsche Zeitung daily reported Wednesday.

Germany sent the two unnamed Russian Embassy employees home because it said Moscow did not sufficiently cooperate with Berlin in its investigation into the August murder of Zelimkhan Khangoshvili. A Russian citizen arrested on suspicion of shooting the Georgian citizen on his way to a mosque in the German capital was reported to have received Russian state support.

“The designated Russians are two employees of the military intelligence service GRU,” SZ reported, saying it obtained the information together with Germany’s NDR and WDR broadcasters.

Federal prosecutors took over the murder investigation, an act that Germany’s interior minister said underscores the seriousness of the crime. The Wall Street Journal reported that Berlin could impose sanctions on Russia for the crime committed on its soil.

German Chancellor Angela Merkel said at a NATO summit in London on Wednesday she would raise the issue with Russian President Vladimir Putin at their planned meeting in Paris next week.

German prosecutors said there were sufficient leads to indicate that either Russia or Chechnya ordered Khangoshvili’s killing. They added that Moscow labeled Khangoshvili, who fought alongside anti-Russia separatists in Chechnya, a terrorist.

The Kremlin denied links to Khangoshvili’s assassination and Russia’s Foreign Ministry vowed to retaliate to the expulsion of its two diplomats.

Following the reports, Interfax cited an unnamed Russian law enforcement source as saying that Khangoshvili had allegedly helped organize and participated in terrorist acts in Russia. Another source said that authorities in southern Russia’s republic of Ingushetia placed him on their terrorism wanted list in 2008.

Another report published Wednesday alleged that the GRU houses a so-called “base camp” in the French Alps. 

At least 15 officers of a GRU unit linked to a campaign to destabilize Europe have either stayed or transited through the base camp in Haute-Savoie, France’s Le Monde newspaper reported

Western nations imposed sanctions on Russia over its 2014 annexation of Crimea and its role in the conflict in eastern Ukraine. Last year they expelled 100 Russian diplomats over the poisoning of a Russian double agent and his daughter in Britain.

Reuters contributed reporting to this article.