The Shot Telegram channel said that Russia had downed more than 200 Ukrainian drones and five U.S.-made ATACMS ballistic missiles.

"The enemy has organized a massive combined strike on the territory of the Russian regions," the Two Majors war blogger said.

Roman Busargin, governor of the Saratov region about 720 km (450 miles) southeast of Moscow, said the cities of Saratov and Engels, on opposite banks of the Volga River, had been subjected to a mass drone attack and there was damage to two industrial sites. Schools had shifted to remote learning, he said.

Ukraine attacked the same region last week and claimed to have struck an oil depot serving an airbase for Russian nuclear bomber planes, causing a huge fire that took five days to put out.

The independent Astra news outlet reported a fire at an industrial site in the city of Kazan, east of Moscow, as a result of a drone attack.

Alexander Bogomaz, the governor of the Bryansk region in western Russia, said Ukraine had launched a major missile attack but did not say which missiles had been used.

Flight restrictions were imposed at airports in Kazan, Saratov, Penza, Ulyanovsk and Nizhnekamsk, Russia's aviation watchdog said.

Nizhnekamsk, in Russia's republic of Tatarstan, is home to the major Taneco refinery. Shot said attack sirens were sounded at the refinery.