A Ukrainian drone struck Russia’s third largest oil refinery on Tuesday about 1,300 km from the front lines, hitting a unit that processes about 155,000 barrels of crude per 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 340,000 barrels per day.

Pictures from the scene indicated the drone hit the primary refining unit, CDU-7, at the refinery, though it appears to have not done serious damage.

An industry source who spoke to Reuters on condition of anonymity 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 half of the plant’s total annual production capacity.

The refinery accounts for about 6.2 per cent of Russia’s refining capacity.