“You will be held accountable one way or another,” Zelensky said on Wednesday.
“Today or tomorrow, it doesn’t matter that much.
“The important thing is that it’s inevitable.”
As an example he mentioned a Russian fighter jet shot down by Ukrainian forces over the besieged city of Mariupol.
“And this will happen to anyone who kills our people, peaceful people in our peaceful country,” the Ukrainian president said.
He added that Russian pilots apparently have no idea of the gravity of the orders they are carrying out.
“The killing of civilians is a crime.”
Ukraine claims to have shot down about 100 Russian fighter planes and bombers since Russia invaded its western neighbour nearly four weeks ago.
The claim could not be verified independently.