A former lawmaker of the Russian State Duma and key witness in a treason case against Ukraine’s ousted leader Viktor Yanukovich was shot dead in the center of the Ukrainian capital of Kiev on Thursday, police said.

Kiev police chief Andriy Kryshchenko told the television channel 112 that Denis Voronenkov was killed around noon and his bodyguard was also injured in the attack.

Voronenkov fled to Ukraine with his wife last year and was helping the Ukrainian authorities build a treason case against Yanukovich.

He has also spoken out against Russia’s annexation of Crimea in March 2014, although he voted for the move at the time.

“A cynical murder of one of the witnesses involved in the state’s case against ex-president Yanukovich,” said Ukraine’s General Prosecutor Yuriy Lutsenko.

Voronenkov had been placed on a Russian federal wanted list in connection with an alleged $5 million property fraud.

Yanukovich fled Ukraine during the 2013-2014 Maidan street protests, which he said were tantamount to a “coup” organized by armed nationalist radicals.

Ukrainian President Petro Poroshenko said that the fatal shooting was an act of Russian “state terrorism.” But the Kremlin slammed the allegations as “absurd.”

Also Thursday, Ukraine’s Chief Military Prosecutor Anatoliy Matios said he is probing a series of explosions that hit a munitions depot in the country’s east overnight.

“A fire broke out … as a result of an act of sabotage at a depot in the town of Balakliya where missiles and munitions were kept,” Matios said in a statement. “The fire led to the detonation of munitions.”

Ukraine’s security services described it a suspected act of “diversion”, while military prosecutors said they had launched a criminal case into possible “negligence” by servicemen.

Matios said witnesses heard a sound resembling that of a drone in flight before the blasts began.

Defense Minister Stepan Poltorak said authorities were considering the theory that “explosive devices dropped from an unmanned aerial vehicle” could have caused the fire.

“We have a ‘friendly’ country – the Russian Federation,” Poltorak said. “I think that first of all it could be representatives who help the (separatist) groups that carry out combat missions,” he said.

Ukraine did not provide evidence of Russian or rebel involvement.

Nobody was hurt. But as of Thursday afternoon 20,000 people living in within a 10-kilometre radius from the depot had been evacuated.

An AFP reporter said local authorities had blocked a road going into Balakliya, which is located some 150 kilometers from eastern Ukraine’s rebel-held regions.

The Ukrainian military has been fighting pro-Russian separatists in the country’s east since April 2014 in a conflict that has killed more than 10,000 people.