On Wednesday, a major Russian oil refinery close to the Ukrainian border in the Rostov region was hit by two drones that allegedly appeared to come from the direction of Ukraine, local authorities claimed.

The attack reportedly sent flames and black smoke billowing into the sky and prompted the plant to stop production.

Russian state news agency TASS cited an unnamed source from local authorities saying that the two Ukrainian drones had flown over the Novoshakhtinsk refinery, which lies 5 kilometers (3.1 miles) from the Ukraine border.

“One of them made an impact, crashing into a heat transfer unit, after which the blaze started. The second one flew away,” the anonymous source told TASS.

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Russia’s ministry of emergency situations for the Rostov region claimed no deaths or injuries were documented but said that 35 people and 17 pieces of equipment were at the location.

Rostov’s regional governor, Vasily Golubev, said the first drone struck at 8.40 a.m. local time, hitting a crude distillation unit. The second strike was 43 minutes later and aimed at crude oil reservoirs at the plant but caused no fire, he said.

Golubev noted fragments of the two drones had been found at the refinery and that the case is currently under investigation.

“Staff has been evacuated, and technological equipment has been stopped to assess the damage,” he said.

The Novoshakhtinsk refinery is the largest supplier of petroleum products in southern Russia and has an annual capacity of up to 7.5 million tons. The plant started operations in 2009.

Russian authorities in regions along the Ukraine border have reported numerous attacks from the country since Moscow invaded its ex-Soviet neighbor.

Among them, videos of alleged explosions in the Kursk region have been posted on social media, two oil depots in Bryansk were said to have been hit by Ukrainian missiles, and an ammunition station reportedly caught fire near the village of Staraya Nelidovka in the Belgorod region.

Kyiv has rejected Kremlin claims that Ukraine is attacking Russian locations near the border.