A former Russian MP has been shot and killed in the centre of the Ukrainian capital of Kiev, in what the Ukrainian president described as an "act of state terrorism" by Russia.
Denis Voronenkov, who testified to Ukrainian investigators and criticsed Moscow's illegal annexation of Crimea, was shot dead by an unidentified gunman near the entrance of an upscale hotel.
The attacker also wounded Mr Voronenkov's bodyguard, who fired back and wounded the gunman.
The alleged attacker has died in hospital, a police spokesman said.
Ukrainian President Petro Poroshenko said the killing "clearly shows the handwriting of Russian special services shown repeatedly in various European capitals in the past."
In a statement released by his spokesman, Svyatoslav Tsegolko, Mr Poroshenko described the victim as a key witness who gave testimony about "Russian aggression" to the Ukrainian authorities.
Russian President Vladimir Putin's spokesman, Dmitry Peskov, dismissed the claim of Russian involvement in the killing as "absurd" in a statement carried by Russian news agencies.
Russian Foreign Ministry spokeswoman Maria Zakharova went further, saying the "killer regime" in Kiev "will do its best to make sure that no one will ever know the truth about what happened."
Another former MP and Kremlin critic living in Kiev said Mr Voronenkov was killed while heading to meet with him.
Mr Voronenkov was "an investigator who was deadly dangerous for the [Russian] security agencies," Mr Ponomaryov wrote on Facebook, according to a translation from The Moscow Times.
Mr Poroshenko said it wasn't accidental Mr Voronenkov's killing came on the same day as the fire that erupted at a Ukrainian military arsenal in the Kharkiv region, which Ukrainian officials said was caused by sabotage.
The Ukrainian president did not provide evidence for his claim.
Ukraine's defence minister has said the country suspects the Russian military or its separatist rebel proxies were responsible for blowing up a warehouse storing tank ammunition in the eastern city of Balaklia.
Fire and explosions caused the detonation of ammunition in several sites at the base, possibly set off by a drone attack or a radio or timed device, Defence Minister Stepan Poltorak said.
Mr Voronenkov, 45, a former member of the communist faction in the lower house of Russian parliament, had moved to Ukraine last autumn and had been granted Ukrainian citizenship.
In addition to criticising Moscow's annexation of Crimea, he had been due to testify against ex-President Viktor Yanukovych, a firm ally of President Vladimir Putin.
He left Russia with his wife, the singer Maria Maksakova, who was also a member of parliament.
He said he had to leave Russia because of persecution by Russian security agencies, and had renounced his Russian citizenship.
After Voronenkov's move to Ukraine, Russian investigators filed fraud charges against Voronenkov in connection with his business activities.
Mr Peskov said Mr Putin was informed about Mr Voronenkov's killing and voiced hope that Ukrainian authorities would solve the crime.
He added Mr Voronenkov's widow was welcome to return to Russia.
