Germany expelled two Russian diplomats on Wednesday after prosecutors said Moscow could be behind the killing of a former Chechen rebel commander in a Berlin park.
Zelimkhan Khangoshvili, a 40-year-old Georgian national, was shot twice in the head at close range in Kleiner Tiergarten park on August 23, allegedly by a Russian man who was arrested shortly afterwards.
The suspect was riding a bicycle and was seen by witnesses afterwards throwing the bike and a stone-laden bag with a gun into a river.
He has been named by police only as Vadim S.
"The foreign ministry has today declared two employees of the Russian embassy in Berlin as personae non grata with immediate effect," the ministry said in a statement.
"Despite repeated high-ranking and persistent demands, Russian authorities have not cooperated sufficiently in the investigation into the murder."
Federal prosecutors in charge of intelligence cases earlier on Wednesday said they had taken over the investigation from Berlin authorities.
"There is sufficient factual evidence to suggest that the killing... was carried out either on behalf of state agencies of the Russian Federation or those of the Autonomous Chechen Republic," the prosecutors said.
The investigative website Bellingcat said on Tuesday the suspect in custody was using a fake identity.
It said he was 54-year-old Vadim Nikolaevich Krasikov and that he grew up in Kazakhstan when it was part of the Soviet Union before spending time in Siberia.
The site said he had previously been accused of murdering a Russian businessman in Moscow in 2013 in which the attacker also used a bicycle to approach the victim.
Russia put Krasikov on an Interpol wanted list but later withdrew his name and "facilitated the issuance of a new, false identity for him", Bellingcat said.
German media said the suspicion was that Russian intelligence agencies had recruited him.
The killing has been compared with the poisoning of former Russian agent Sergei Skripal in Britain last year with a nerve agent, widely blamed on Russian intelligence.
Relations between Britain and Russia plunged into a deep freeze after the incident, which led to the expulsion of dozens of Russian diplomats around the world.