Several people were killed in Russia on Sunday as a result of Ukrainian drone attacks.
The strikes damaged civil infrastructure in the southern cities of Engels and Saratov on the Volga River, Roman Busargin, governor of the Saratov region, said on Telegram.
Two people were killed in Engels where a multi-storey residential building was damaged, he said.
Engels is home to one of the largest air force bases in Russia. Strategic bombers regularly take off from there to launch missile strikes on cities in Ukraine, which has made the city a prime target of Ukrainian counter-attacks on several occasions.
Unverified footage circulating on social media showed fires on the grounds of the Saratov refinery, which has frequently been the target of Ukrainian attacks.
Russian media reported that three people had died in both Belgorod and Udmurtia, while at least five others were injured by Ukrainian missiles and drones. The authorities did not provide any further details.
Udmurtia is some 1,300 kilometres from the Ukrainian border.
Ukrainian President Volodymyr Zelensky confirmed Ukrainian attacks on targets in Russia, naming the Saratov oil refinery and the Engels military airbase. He thanked the Ukrainian armed forces and said that Ukraine was taking the war back to where it had come from.
Ukrainian drones also targeted a logistics facility in the Samara region operated by online retail giant Wildberries, the company said.
A fire broke out on site, but no one was injured, according to Wildberries, whose operations have been repeatedly targeted by Ukraine in recent weeks.
A total of 635 Ukrainian drones were intercepted over Russian territory and the annexed Crimean Peninsula overnight, according to the Defence Ministry in Moscow.
The figures cannot be independently verified, but they do indicate the intensity of the attacks.
Ukraine has been defending itself against a full-scale Russian invasion for more than four years. As part of its defensive campaign, it is also targeting locations deep within Russian territory, recently stepping up its counter-attacks, primarily using drones.