The Slavyansk oil refinery in Russia's Krasnodar region has been forced to suspend some operations after being damaged in a Ukrainian drone attack, the state TASS news agency cited an executive overseeing the plant as saying on Saturday.

On the back foot on the battlefield in some places, Ukraine has been systematically targeting Russian energy infrastructure facilities - despite U.S. requests for it to not do so - in an attempt to disrupt Russia's economy and therefore its ability to fund its war effort.

A Ukrainian intelligence source told Reuters that Ukraine had attacked the Ilsky and Slavyansk oil refineries in Russia's Krasnodar region with drones early on Saturday, causing fires at the facilities.

The same source said Ukrainian drones had also targeted the Kushchevsk military airfield in the same region overnight.

Russia's Defence Ministry said its air defence units had destroyed 66 Ukrainian drones over the territory of the Krasnodar region, and two more over the Crimean peninsula, which Russia annexed from Ukraine in 2014.

"The work of the (Slavyansk) plant has been partially suspended. Exactly 10 UAVs (drones) flew directly into the plant, there was a strong fire. There may be hidden damage," Eduard Trudnev, the security director at Slavyansk ECO Group, which operates the plant, was cited as saying by TASS.

Earlier on Saturday, Roman Siniagovskyi, a local government official in Slavyansk, said on his official Telegram channel that the refinery's storage tank facilities had not been damaged but that a distillation tower had been hit.

He said a fire caused by the attack had been put out and that nobody had been injured.

(Reporting by Reuters; Writing by Andrew Osborn Editing by Tom Hogue and Toby Chopra)