A Russian man goes on trial Wednesday accused of assassinating a former Chechen commander in a Berlin park on Moscow's orders, a case that has cast a pall over ties between Russia and Germany.

Vadim K., also known as Vadim S., stands accused of gunning down a Georgian national identified by German authorities as 40-year-old Tornike K., in Kleiner Tiergarten park on August 23 last year.

German prosecutors, who do not release the full names of suspects ahead of criminal trials, have said the contract killing was carried out at the behest of Russia, prompting Berlin to expel two Russian diplomats. 

Moscow has denied the allegations, taking tit-for-tat action against Berlin.

Chancellor Angela Merkel said in May that the killing "disrupts cooperation of trust" between Berlin and Moscow and some analysts have suggested the murder has led to a change in her approach towards Russia. 

The German leader has always stressed the importance of keeping dialogue open with her Russian counterpart Vladimir Putin, but she has sharpened her tone in recent months. 

The trial comes at a time of European anger with Russia over the poisoning of Kremlin critic Alexei Navalny, who is receiving treatment in the German capital. 

Germany has said that tests it carried out found that the 44-year-old was poisoned with the Soviet-era deadly nerve agent Novichok. 

France and Sweden have corroborated the finding, which activists say puts responsibility for the murder attempt squarely on Moscow. 

Merkel's government has not ruled out pushing for sanctions from the European Union over the attack. 

- FSB link? -
With tensions running high, Wednesday's trial will likely be closely scrutinised for details about Moscow's involvement.

Investigative website Bellingcat named the suspect as 54-year-old Vadim Krasikov, who grew up in Kazakhstan when it was part of the Soviet Union before moving to the Russian region of Siberia.

He received training from Russian intelligence service FSB and was part of its elite squad, the website said.

Days before the killing, he had posed as a tourist, visiting sights in Paris including the Eiffel Tower before travelling to Warsaw, according to a separate report in Der Spiegel weekly.

He also toured the Polish capital before vanishing on August 22, without checking out from his hotel, the report said.

A day later, riding a bicycle in Berlin's Kleiner Tiergarten park, the suspect approached the victim from behind, firing a Glock 26 pistol equipped with a silencer at the side of Tornike K.'s torso, German prosecutors said.

After the victim fell to the ground, the accused fired another two shots at his head that killed the Georgian on the spot.

He was seen throwing a bag into the nearby Spree river from where police divers later recovered the Glock handgun, a wig and bicycle.

The suspect was arrested after the killing, which took place just minutes away from the chancellery and the German parliament.

Investigators later found his mobile phone and a return flight ticket for Moscow in August 25 in his hotel room in Warsaw, Spiegel reported.

- 'Very cruel' -
Russian President Vladimir Putin had described the victim as a "fighter, very cruel and bloody" who had fought with separatists against Russian forces in the Caucasus and also been involved in bombing attacks on the Moscow metro.

Moscow also said it had been seeking his extradition.

Named as Zelimkhan Khangoshvili by German media, the victim had survived two assassination attempts in Georgia.

Following that, he sought asylum in Germany and had spent the past years in the country.

Both the killing and Navalny's poisoning have been compared with the poisoning of former Russian agent Sergei Skripal in Britain in 2018, also widely blamed on Russian intelligence.

Russia has for years drawn the ire of Western powers, from annexing Ukraine's Crimea to meddling in elections and backing President Bashar al-Assad's government in Syria.