A prominent journalist working for the online investigative newspaper Ukrayinska Pravda was killed by a car bomb in central Kiev early on Wednesday morning.
Pavel Sheremet was driving to work in the car of the newspaper's owner when it was blown up, an adviser to Interior Minister Anton Gerashchenko said.
Two eyewitnesses told Reuters television they had heard a loud blast and seen an explosion from underneath the car, which lay charred in the middle of the street.
"I'm in shock, I don't know what to say, it is a matter of honor for the police to investigate the case," the head of the national police force, Khatia Dekanoidze, told reporters. "I will personally take charge of the case."
Prime Minister Volodymyr Groysman posted a message on Facebook saying: "The day has begun with terrible news. The prominent Ukrainian journalist Pavel Sheremet was killed this morning."
The founder of Ukrayinska Pravda, Georgiy Gongadze, was an investigative journalist who was murdered 16 years ago. The incident helped to precipitate Ukraine's Orange Revolution. His body was found decapitated in a forest outside Kiev.