Vladlen Tatarsky, a well-known military blogger in Russia, was killed in a cafe explosion, according to the Russian Interior Ministry.
A bombing at Street Food Bar No. 1 left at least 19 people hurt.
Social media videos depict an explosion and injured people on the ground. It is unclear who was in charge of the explosion.
Vladlen Tatarsky (real name Maxim Fomin) was a vocal supporter of Russia’s war in Ukraine.
He was a guest speaker at an event hosted by the cafe when the bomb went off.
He had provided front-line coverage from the Ukraine and rose to prominence last year after posting a video shot inside the Kremlin in which he said “Everybody will be defeated, every person will be killed, and every person will be robbed as necessary. Exactly how we like it.”
President Vladimir Putin hosted a ceremony in the Kremlin on that occasion, where he announced Russia’s annexation of four partially occupied regions of Ukraine. International organisations condemned that land grab. President Putin was born and raised in St. Petersburg, where he first attained notoriety.
A bomb was allegedly concealed in a statue that was given to Tatarsky in a box as a gift, according to interior ministry sources cited by Russia’s RIA news agency.
According to the St. Petersburg news outlet Fontanka, Yevgeny Prigozhin, the leader of Russia’s infamous Wagner mercenary group, had previously owned the café that was attacked on Sunday.
On Telegram, Tatarsky has more than 500,000 followers. Aspects of the Russian campaign in Ukraine have been criticised by him and other military bloggers.
On Telegram, a group going by the name Cyber Front Z claimed to be “Russia’s information troops” and claimed to have rented out the cafe for the evening.
“There was a terrorist attack. We took certain security measures but unfortunately they were not enough,” its post on Telegram said. “Condolences to everyone who knew the excellent war correspondent and our friend Vladlen Tatarsky,” it said.
Last August a car bomb attack near Moscow killed Darya Dugina, a journalist and prominent supporter of the Russian military. She was the daughter of ultra-nationalist philosopher Alexander Dugin, a close ally of Mr Putin.