The Russian Belgorod region bordering Ukraine was hit by strikes on Sunday, leaving at least four people injured in the latest attacks in the area, Russian officials said.
Around 16 explosions were recorded in the city of Belgorod, Russia's investigative committee, which investigates serious crimes, said Sunday.
The city of 330,000, around 40 kilometres (25 miles) from the Ukrainian border, had until recently rarely been hit, unlike the surrounding region.
The attacks come a day after an oil depot was hit in the same area.