Well-known Russian military blogger Vladlen Tatarsky was killed in a bomb blast in a cafe in St Petersburg on Sunday (local time), Russian news agencies reported.
They quoted the interior ministry as confirming the death of Tatarsky and saying that 16 people had been wounded.
Tatarsky, whose real name was Maxim Fomin, had more than 560,000 followers on Telegram and was one of the most prominent of the influential military bloggers who have provided an often critical running commentary on Russia's war in Ukraine.
He was among hundreds of attendees at a lavish Kremlin ceremony last September to proclaim Russia's annexation of four partly occupied regions of Ukraine, a move that most countries at the UN condemned as illegal.
"We'll defeat everyone, we'll kill everyone, we'll rob everyone we need to. Everything will be as we like it," he was shown saying in a video clip on that occasion.
A St Petersburg website said the explosion on Sunday took place at a cafe that had at one time belonged to Yevgeny Prigozhin, founder of the Wagner private army that is fighting for Russia in Ukraine.
There was no indication who was behind the blast.
If Tatarsky was deliberately targeted, it would be the second assassination on Russian soil of a high-profile figure associated with the war in Ukraine.
Russia's Federal Security Service accused Ukraine's secret services last August of killing Darya Dugina, the daughter of an ultra-nationalist, in a car bomb attack near Moscow that President Vladimir Putin called "evil".
Ukraine denied involvement.
Reuters