Series of blasts were heard in the early hours of Wednesday in three Russian provinces bordering Ukraine, authorities said, and an ammunition depot in the Belgorod province caught fire around the same time.
Belgorod regional governor Vyacheslav Gladkov said a fire at the ammunition depot near the Staraya Nelidovka village had been extinguished and no civilians have been injured.
Russia this month accused Ukraine of attacking a fuel depot in Belgorod with helicopters and opening fire on several villages in the province.
The Belgorod province borders Ukraine's Luhansk, Sumy and Kharkiv regions, all of which have seen heavy fighting since Russia invaded Ukraine two months ago.
Separately, Roman Starovoyt, the governor of Russia's Kursk province, which also borders Ukraine, said that explosions had been heard in Kursk city early on Wednesday which were most likely the sounds of air defence systems firing.
In Voronezh, the administrative centre of another province adjacent to Ukraine, Russia's TASS news agency cited an emergencies ministry official as saying that two blasts had been heard and the authorities were investigating.
Russia sent tens of thousands of troops into Ukraine on February 24 in what it called a "special operation" to degrade its military capabilities and root out what it calls dangerous nationalists. Ukrainian forces have mounted stiff resistance and the West has imposed sweeping sanctions on Russia in an effort to force it to withdraw its forces.
Rescuers search for 140 people after Indonesia ferry hits bad weather
Philippine ferry fire victims may take months to identify, authorities say
Saudi Arabia shuts key oil pipeline after drone attack
BRICS members agree joint declaration at New Delhi summit
Death toll in Philippine ferry fire rises to 76 as rescuers recover more remains
