A drone attack on the Ilsky oil refinery in southern Russia, the second in as many days, has caused a fire, TASS news agency reported on Friday, citing emergency services.

Russia's RIA Novosti news agency also reported that there were no casualties following Friday's incident, while the fire had been put out.

It was not immediately clear who was behind the incident. Ukrainian officials do not usually claim responsibility for such attacks inside Russia's territory, although they sometimes celebrate them using euphemistic language.

A source at refinery told Reuters that an aerial cooler at the CDU-5 column, which has an annual capacity is 1.8 million tonnes, was hit. Another primary unit at the plant has capacity of 3.6 million tonnes per year.

That cooler could be replaced within a couple of weeks, though the impact is yet to be fully accessed, the source added.

The press service at the plant was not immediately available for comments.

The Ilsky refinery, near the Black Sea port of Novorossiisk in the Krasnodar region, has a processing capacity of around 6.6 million tonnes per year.