A massive Ukrainian drone attack on the city of Nizhnekamsk in Russia's Tatarstan has killed at least 13 people, the authorities said on Monday.

The head of the Tatarstan Republic, Rustam Minnikhanov, declared a period of mourning following the attack.

Another 78 people required medical attention, with 25 hospitalized, according to his government, which is based in the major city of Kazan.

Nine people were killed in a workers' hostel that was severely damaged in the attack, state news agency TASS reported, citing local authorities.

Among the victims were citizens of Uzbekistan and Tajikistan, it said.

The mayor of Nizhnekamsk, Radmir Belyayev, reported a major attack by Ukrainian drones on industrial facilities and civilian targets. Ukrainian media reported that one of the largest oil refineries in the area was targeted.

The General Staff in Kiev later confirmed the attack on the Taneko refinery in Nizhnekamsk.

Ukrainian drones also targeted the Western Siberian region of Tyumen.

Regional Governor Alexander Moor said a fire broke out after "several drones" had crashed on the premises of an industrial plant. He did not provide any details regarding the plant's location.

However, videos circulating on social media showed flames at a refinery in Tobolsk, according to media reports. The industrial city is located more than 2,000 kilometres from Ukraine.

The General Staff in Kiev later confirmed an attack on a petrochemical plant in Tobolsk. It said that the plant produces raw materials of military importance.

In its defensive struggle against Moscow's invasion, Kiev is targeting facilities belonging to the Russian oil industry.

The aim is to deprive the Russian war machine of vital revenue, such as that derived from energy exports. Recently, an increasing number of civilians have been killed in Ukrainian counter-attacks.

Ukraine also reported injuries on Monday, with 13 wounded in a Russian airstrike on the south-eastern city of Zaporizhzhya.

The region's military governor, Ivan Fedorov, said a glide bomb was dropped on the industrial city, causing damage to residential buildings and cars.

The city is under almost constant air-raid alarms, with the front line just 20 kilometres away.