According to Vyacheslav Gladkov, the regional governor, at least three people were killed in explosions in Belgorod in Russia, which is near the border with Ukraine.
He said that the blasts had partially destroyed 11 apartments buildings and at most 39 private residential properties.
He added that the explosions activated air defense systems.
The statement of the governor could not independently be confirmed, and there was no immediate response from Ukraine.
This information was obtained from the Telegram social media app, Mr Gladkov.
Russia invaded Ukraine on February 24, claiming that it wanted to "demilitarise and de-Nazify" Ukraine. Thousands of civilians and combatants were killed or injured as a result, and at least 12,000,000 people fled their homes.
The West has responded by arming Ukraine, and imposing unprecedented sanctions against Russia, a global superpower and energy supplier.
