Russia has announced a drone attack on a number of regions. Explosions were heard in Rostov-on-Don, Novomoskovsk, Tula region and Engels, Saratov region. In the Kaluga region, an "industrial facility" caught fire as a result of the attack, and in Volgograd, an oil refinery was targeted.

As the head of the Central Oil and Gas Development Agency, Andrey Kovalenko, writes, the Volgograd refinery is an important target, as it is among the top 10 oil refineries in Russia.

"This is not the first attack, the Russians are trying their best to protect it," Kovalenko noted.