A general view shows the Russian embassy. File photo: REUTERS/Fabrizio Bensch.

Berlin - Suspicions of Russian state involvement in an apparent contract killing of a Georgian man in central Berlin earlier this year have led Germany to expel two Russian diplomats.

The diplomats have been designated as personae non gratae, the German Foreign Ministry said on Wednesday, adding that the government suspects Russian intelligence agencies were involved in the shooting.

Russia's Foreign Ministry condemned Germany's move as "unfriendly" and "baseless," according to comments carried by Russian news agencies.

Russia's top diplomat, Foreign Minister Sergei Lavrov, said the country was preparing its official response.

Senior Russian lawmaker Leonid Slutsky, an authority on foreign policy, said Germany should expect to have two of its diplomats expelled from Russia as a "symmetrical" measure.

The German authorities moved ahead of a summit on Ukraine to be attended by Russian President Vladimir Putin and German Chancellor Angela Merkel, along with French President Emmanuel Macron, in Paris on Monday.

Commenting about the case on the sidelines of a NATO summit in Britain, Merkel criticized Russia for giving insufficient assistance to German investigators.

"In bilateral relations, it is of course notable that we unfortunately received no active help in clarifying this incident," Merkel said.

Germany's decision to expel the two Russian diplomats was taken because of the lack of assistance, Merkel said, adding that the measure was not expected to affect the Ukraine summit.

Germany's federal prosecution service has taken over responsibility for the probe into the shooting, which occurred in broad daylight on August 23 in a small park in the inner-city neighbourhood of Moabit.

The killer, riding a bicycle, approached the 40-year-old victim from behind and aimed at his back and head.

German federal prosecutors investigate cases where there is firm suspicion of involvement by a foreign power. The espionage department of the Federal Prosecutor's Office in the western city of Karlsruhe will work on the case.

The German investigation is also looking into a possible link to officials in Chechnya, a republic within the Russian Federation that has its own constitution but is still controlled by Moscow.

Russia has fought two wars to quell separatist rebellions in Chechnya since the dissolution of the Soviet Union almost three decades ago.

A man with a Russian passport has been detained in connection with the Berlin killing. The suspect, also implicated in the murder of a Russian businessman in 2013, has maintained his right to keep silent.

The victim killed in August is said to have fought against Russia on the side of Muslim Chechens in the early 2000s. He is also reported to have survived a May 2015 attempt on his life in the Georgian capital, Tbilisi.

Putin's spokesman on Wednesday adamantly denied Russian state involvement in the murder.

"What does this have to do with the Russian authorities? These are absolutely baseless assumptions," Kremlin spokesman Dmitry Peskov said in comments carried by Russian news agency Interfax.

"This topic is somehow exalted by the German media, but that does not mean this is the case," Peskov said.

Over the past two days Russian and German law enforcement authorities have met in Moscow to discuss collaboration, Russia's prosecutor general's office said in a statement. It did not mention the murder case.

dpa