At least 13 people have been killed and 75 others injured in a Ukrainian drone strike on Russia's Tatarstan region, Russian officials said.
A child was among those killed in the attack on the city of Nizhnekamsk, in one of the deadliest single strikes on Russian territory since Moscow launched its full-scale invasion of Ukraine.
The city is located more than 1,100 kilometres (680 miles) from the Ukrainian border.
Ukraine has not officially commented on the reported casualties, but its armed forces confirmed that the Tanevo oil refinery in Nizhnekamsk was hit.
Ukrainian defence technology company FirePoint said its FP-1 drones were used in the attack.
Strike lasted several hours
The attack reportedly continued for several hours overnight and into the morning.
Images verified by the BBC showed large plumes of smoke and flames rising over the area, while air raid sirens could be heard in the background.
Russian authorities said industrial facilities as well as residential areas were targeted.
Russia's Investigative Committee said civilians who were not involved in military operations were among those affected. The BBC said it could not independently verify the claim.
Tatarstan's head, Rustam Minnikhanov, confirmed the attack and offered condolences to the families of those killed.
Nizhnekamsk Mayor Radmir Belayev described the incident as "a tremendous pain for all of us."
A period of mourning has been declared across Tatarstan.
Ukraine steps up long-range strikes
Ukraine has increasingly carried out long-range drone attacks against Russian energy facilities, warehouses and other infrastructure that Kyiv says contributes to Moscow's war effort.
The Tanevo refinery in Nizhnekamsk was previously targeted by Ukrainian defence forces on June 12.
Russia said its air defences shot down more than 450 Ukrainian drones overnight, although details about how many were involved in the Tatarstan attack were not immediately clear.
The strike comes amid continued heavy fighting between Russia and Ukraine.
Russia has also continued launching large-scale missile and drone attacks against Ukrainian cities. A combined attack on Kyiv last week killed 21 people, while five people were killed in a Russian artillery strike on Kharkiv, according to Ukrainian authorities.
The latest attacks underscore the growing reach of Ukrainian drone operations deep inside Russian territory, while civilian casualties continue to rise on both sides of the conflict.
