A Russian MP who fled Moscow fearing for his life at the hands of President Putin's secret service was assassinated today in the Ukrainian capital Kiev.
Denis Voronenkov, who had testified against the pro-Russian former Ukrainian President, Viktor Yanukovych, was shot dead in broad daylight by an assassin with a 9mm handgun.
His bodyguard was injured but fired back, fatally wounding the gunman, who died a few hours later.
The 45-year-old fled Moscow in October with his wife Maria Maksakova, an opera singer, saying they were fed up of the 'schizophrenic' Russian government.
Maksakova, who had a son with Voronenkov last year, rushed to the scene of the shooting outside a luxury hotel today and broke down in tears.
Ukraine's President Petro Poroshenko said it was an 'act of state terrorism' by Russia and added: 'It clearly shows the handwriting of Russian special services shown repeatedly in various European capitals in the past.'
But Kremlin spokesman Dmitry Peskov said: 'We believe that all the falsehoods that can already be heard about much-hyped Russian involvement are absurd.'
The bodyguard remains in hospital and the assassin has not yet been identified.
Nikolai Kovalyov, a former Russian security chief who is now an MP, told Russian state television the killing could have been rooted in a business dispute.
Ukrainian Prosecutor-General Yuriy Lutsenko blamed the Kremlin for Voronenkov's killing, saying Russia wanted to punish him for his testimony to Ukrainian investigators.
He said it was a 'cynical murder' of a man who had provided investigators with important testimony about Russian aggression and added: 'This was a typical show execution of a witness by the Kremlin.'
The killing came a few hours after Russian or separatist saboteurs blew up a warehouse storing tank ammunition at a military base in the east of the country.
In Voronenkov's last interview, with Radio Free Europe last month, he said he opposed 'Russia's war' against Ukraine but said it would only end when Putin left the scene.
He also threatened to testify about the involvement of former President Yanukovych - an ally of Putin - in the separatist uprising in eastern Ukraine and said: 'I will talk about criminal deeds of the former president, which led to the ongoing bloodshed in Donetsk and Luhansk regions.'
At the end of the interview with Kiev-based journalist Christopher Miller Voronenkov and his wife laughed as they showed him social media messages calling them 'traitors'.
Miller wrote: 'Maksakova...says of all the attention they have gotten in the past 48 hours: "God, it's so funny!"'
Kiev-based journalist Christopher Miller tweeted: 'As Ukraine's president and prosecutor general jump to cast Voronenkov murder as Kremlin plot, Kiev police tell me still too early to call.'
He added: 'Yes, Voronenkov was viewed in Moscow as traitor - no worse crime. But had enemies in Ukraine unhappy he was welcomed here, given citizenship.'
Voronenkov was wanted in Moscow on fraud charges and Russian media had reported in recent months that he owned five expensive Russian apartments and a fleet of luxury cars.
His name also surfaced in the Panama Papers leak as a shareholder of a company based in the British Virgin Islands.
He said he feared Russia's Federal Security Service (FSB), which took over from the KGB in the 1990s.
Last month, in an interview with Radio Free Europe, Voronenkov compared Putin's Russia with Nazi Germany and said the annexation of the Crimea in 2014 was 'illegal' and a 'mistake'.
In that interview he said he was not interested in Ukrainian politics and only wanted to raise the couple's son, whose first birthday will be next month.
Russia and the Ukraine have been virtually at war with each other since President Yanukovych was ousted by Ukrainian nationalist demonstrators in February 2014.
Ethnic Russian separatists have set up a rebel republic in the Donbass region of eastern Ukraine and Russia annexed the Crimea, which is dominated by ethnic Russians, in the summer of 2014.
Yesterday the Ukraine forbid Russia's entry to the Eurovision Song Contest, Yulia Samoylova, from taking part in the competition in May because she had toured in the 'occupied' Crimea.