"I ordered law enforcement agencies to immediately investigate this crime. Those responsible should be punished," Poroshenko wrote on Facebook.
"A terrible tragedy in Kyiv. That's a shock - I have no other words," the president wrote.
As UNIAN reported earlier, a Ukrainian journalist of Ukrainska Pravda Pavlo Sheremet was killed early Wednesday in a car blast in Kyiv.
Ukraine's Prosecutor General Yuriy Lutsenko said that the journalist's car was blown up by an explosive device.