A top Ukraine security official delivered a sinister warning Tuesday to government critics after the recent murders of three opposition figures. Pro-Russian journalists Oles Buzina and Serhiy Sukhobov and former politician Oleh Kalashnikov were all killed last week by unknown assailants.

“I think that in our time, when there is practically a war going on, Ukrainophobes, if they don’t shut their mouths, should at least stop the rhetoric. I think that in the present situation, there shouldn’t be anyone stepping out directly against Ukraine and Ukrainianness,” security services chief Vasily Vovk said on television, according to Kremlin-owned Russian outlet Sputnik News.

Ukrainian authorities have yet to determine who was responsible for the opposition voices' murders. “Foreign agents” may have played a role,” Vovk reportedly said.

Buzina was a well-known newspaper columnist and editor with distinct pro-Russian views. Kalashnikov was a former member of parliament from the party of ousted President Viktor Yanukovych, who was driven from power in 2014 by a series of pro-democracy protests. Sukhobov was a freelance journalist who advocated for Russia.

Buzina and Kalashnikov were alleged participants in the “Anti-Maidan” movement, in which pro-Russian advocates opposed the demonstrators camped out in Kiev's main square who sought increased integration with the West as part of the “Euromaidan” movement. Some pro-Kremlin activists attacked those who protested Yanukovych’s ties to Moscow, with Buzina and Kalashnikov serving as witnesses in two such criminal cases, Reuters reported.

Buzina was killed on April 16 by two masked gunmen in Kiev, hours after Kalashnikov was murdered at his apartment complex in the same city. Sukbohov was killed at some point between April 13 and April 15.

A European Union representative condemned the murders in a statement last week. “We call for independent and transparent investigations of these cases so that those responsible can be brought to justice. Our sincere condolences go out to the families and friends of the victims,” EU spokeswoman Maja Kucijancic said.