The International Press Institute (IPI) today called upon Ukrainian authorities to immediately investigate the murders of journalists Oles Buzina and Sergey Sukhobok.

According to news reports, Buzina was killed by two masked men at 1:20 p.m. on April 16, while jogging near his home in Kiev. Aged 45, he was an author and TV presenter and was reported to be well known for writing pro-Russian opinion pieces in the daily Segodnya. Buzina had also unsuccessfully stood in last year’s parliamentary election as a candidate with the Russian Bloc party.

As several media outlets noted, several hours earlier, on the evening of April 15, the ex-parliamentary deputy Oleh Kalashnikov, a supporter of former Ukrainian president Viktor Yanukovich, was shot dead while entering his apartment. In comments carried in the press, both Ukrainian President Peter Poroshenko and Russian President Vladimir Putin separately appeared to suggest a link between the killings of Buzina and Kalashnikov, though the two leaders offered contrasting interpretations of the events. Poroshenko characterised the murders as a “deliberate provocation” meant to destabilise Ukraine while Putin suggested they were “politically motivated”.

Sukhobok, 50, was the founder of the news websites ProUA and Okbom and had worked in journalism since 1998. Originally from Donetsk, Sukhobok is reported to have been killed on April 13, in Kiev, although the details of his death – including the manner in which it occurred – remain uncertain.

“International humanitarian law stresses the importance of ensuring respect for fundamental human rights, such as the right to free expression, in times of armed conflict,” IPI Executive Director Barbara Trionfi said. “It further clearly highlights states’ responsibility in this area. Bringing the perpetrators of such violations to justice is therefore a necessary step to show that attacks on journalists because of their opinions will not be tolerated.

“The free circulation of ideas and opinions, and respect thereof, is the first step towards the resolution of any conflict.”

According to IPI’s Death Watch, 19 journalists have now been killed in Ukraine since 1997. Nearly half of these killings – seven – occurred in 2014 alone. Most recently, the photographer Serhiy Nikolayev was killed on Feb. 28 in crossfire between Ukrainian troops and pro-Russian separatists in Peski.