Authorities in Russia’s southern Krasnodar region have raised the alert level in Gelendzhik and Novorossiysk over an oil spill after fuel oil washed ashore and satellite images showed pollution spreading along the Black Sea coast.

Governor Veniamin Kondratyev issued an order warning of a potential emergency in the two cities. He attributed the spill to “accidents” involving vessels targeted by Ukrainian naval drones on Oct. 6.

The order calls for increased environmental monitoring and surveillance of potential industrial hazards. It also recommends that the regional branch of Russia’s Marine Rescue Service take measures to prevent oil from reaching the shoreline.

Fuel oil has already been found along roughly 500 meters of coastline near Novorossiysk, the city’s chief rescue official, Alexei Oderov, said.

Local residents have also reported pollution on the shore. Olga Kotlyar, head of the Abrau-Dyurso rural district, appealed for volunteers to help municipal workers clean up a beach.

Birds with reported chemical burns from petroleum products have been found in Gelendzhik and the nearby resort village of Arkhipo-Osipovka.

The satellite monitoring project Transparent World earlier reported that an image taken overnight on Oct. 10 showed a large oil slick between Arkhipo-Osipovka and Novorossiysk.

Over the following two days, the slick broke into smaller patches and spread as far as Anapa, the project said. It also identified oil traces near Novorossiysk Bay and the Caspian Pipeline Consortium’s offshore loading facilities.

Transparent World linked the pollution to the Oct. 6 naval drone attack on the tanker Aframax Rio off Sochi. The vessel can carry up to 100,000 metric tons of oil, though its cargo at the time of the attack has not been independently confirmed.

The Mash Telegram channel, citing unnamed sources, reported that the tanker was fully loaded.

The attack triggered a major fire that blanketed Sochi in black smoke. The blaze was extinguished the following day.

Authorities closed beaches in Sochi and the neighboring federal territory of Sirius after the attack, but reopened them on Oct. 8, saying tests had found no oil contamination in local waters.

Russia’s consumer protection watchdog Rospotrebnadzor said seawater samples from all districts of Sochi met sanitary standards.