Ukrainian drones have struck one of Russia's biggest refineries, 1300km (800 miles) from the front lines, hitting a core unit which processes about 155,000 barrels of crude refining a day, though an industry source said the damage was not significant. 

Russian officials said its jamming devices locked onto a Ukrainian drone near Tatneft's Taneco refinery, which has an annual production capacity of more than 17 million tons (340,000 barrels per day).

Pictures from the scene indicated the drone hit the primary refining unit, CDU-7, at the Taneco refinery. The unit accounts for around a half of the plant's total annual production capacity.

An industry source said the damage to the unit was not critical while the personnel was returning to the plant.

A fire broke out at the refinery but was extinguished within 20 minutes, the state news agency RIA said, adding that output had not been disrupted.

Ramil Mullin, the mayor of Nizhnekamsk in the Tatarstan region southeast of Moscow where the refinery is located, said there had been no serious damage done.

The unit that was hit accounts for around a half of the plant's total annual production capacity. The refinery accounts for about 6.2 per cent of Russia's refining capacity.

A military intelligence source in Ukraine, which has been at war with Russia since Moscow began a full-scale invasion of its neighbour two years ago, said in Kyiv that the primary Taneco refining unit had been hit, causing a fire.

The source said the aim of the strike was to reduce Russia's oil revenue.

Another Ukrainian intelligence source said Ukrainian-made drones also hit a Russian plant producing long-range "Shahed" attack drones, causing "significant damage".

The attack was one of several in Tatarstan, a highly industrialised region, in the early hours of Tuesday. The Washington Post reported last year that Russia was mass-producing drones at a plant in Tatarstan.

Ukraine has in recent months begun attacking the oil refineries of Russia, the world's second largest oil exporter, impacting Moscow's highly lucrative trade in refined products.

According to Reuters calculations, around 14 per cent of Russia's refining capacity has been shut down by drone attacks. There is more demand for refined oil products than for Russian crude.

The attacks on Russian refineries – many deep inside the world's largest country – have raised concerns in Washington about the potential for escalation with Russia, which is the world's largest nuclear power.

Ukraine says its drone attacks on Russia are justified because it says it is fighting for survival and has suffered widespread damage from to its infrastructure, including power plants, from Russian air strikes.

Ukraine, which says it has been attacked by more than 4630 Russian long-range Shahed drones during the 25-month-old war, regards its own drone production push as a way to hit back at a much better armed and larger enemy.

When asked if Russia thought the United States was involved in the attacks on Russian refineries, the Kremlin said the question was better addressed to the defence ministry and security services.

"The Kyiv regime continues its terrorist activity," Kremlin spokesman Dmitry Peskov said.

"We and our military are primarily working to minimise this threat, and subsequently to eliminate it."

Since President Vladimir Putin ordered the full-scale invasion of Ukraine in 2022, drones have played a major part in the war – either as "kamikaze" attackers or as eyes in the sky that guide in other weaponry to kill soldiers or destroy equipment.

Ukraine has carried out a series of high-profile attacks deep inside Russia, aimed at either undermining Russia's war machine or, as was the case in a 2023 drone attack on the Kremlin, bringing the reality of war to the very heart of Russia.

A powerful ally of Putin said  that NATO was basically fighting Russia in Ukraine and that the US-led military alliance had helped organise strikes on sovereign Russian territory.

Ukrainian sources say they are responsible for the planning and execution of the drone attacks inside Russia. The United States has repeatedly said that it does not support Ukrainian strikes inside Russia.

Tuesday's attacks hit enterprises in Yelabuga and Nizhnekamsk and some people were injured, Tatarstan's head Rustam Minnikhanov said.

Two drones attacked a dormitory on the territory of the Alabuga Special Economic Zone. At least seven people were injured, Russian media reported.