Ukraine's prosecutor general today accused Russia's intelligence agency of hiring a crime boss to organise the murder of a former Russian MP and prominent Kremlin critic in Kiev in March.
Denis Voronenkov, 45, was gunned down in broad daylight in what Ukrainian officials said at the time appeared to be a contract killing.
Ukrainian Prosecutor General Yuriy Lutsenko accused the FSB of hiring a Russian crime boss from the Siberian city of Bratsk named Vladimir Tyurin to organise the killing.
Lutsenko said Tyurin, who is believed to be living in Russia, was used because he had "a personal motive to commit the murder -- eight years ago, he was the common-law husband of (Voronenkov's wife) Maksakova."
Kremlin spokesman Dmitry Peskov had initially dismissed Kiev's accusations that Russia was involved in the murder as "absurd", but there has been no comment on the latest allegations.
Lutsenko said he would submit his findings to a Ukrainian court.
The murder came as Moscow and Kiev remained locked in a bitter feud over Russia's annexation of Crimea and its alleged support of an armed insurgency in eastern Ukraine that has claimed more than 10,000 lives.
The gunman -- a Ukrainian national -- later died in hospital after he was shot by Voronenkov's bodyguard.
Voronenkov fled Russia last October for Ukraine with his wife Maria Maksakova, a former lawmaker and celebrated opera singer, and became a fierce critic of Moscow's annexation of Crimea.
Voronenkov received Ukrainian citizenship in December after testifying against Viktor Yanukovych -- the Kremlin- backed former president of Ukraine living in self-imposed exile in Russia. He is being tried in absentia in Kiev on treason charges.
Lutsenko said Voronenkov's slaying was tied to his "testimony about the presence of Russian troops in Ukraine, as well as to his involvement in the treason trial of Viktor Yanukovych."
Yanukovych's ouster in a 2014 pro-EU revolution was followed by what Kiev's pro-Western leaders call Russia's armed invasion of Ukraine's eastern industrial heartland in retaliation.
The Kremlin denies any involvement in the invasion, despite overwhelming eyewitness evidence of its tanks and troops crossing the Russian-Ukrainian border into the war zone since fighting broke out in April 2014.
Voronenkov told Ukrainian media in February he had repeatedly received death threats from Russian security services.