MOSCOW, July 17 (Reuters) - A chartered oil tanker loading oil at a terminal off Russia's Black Sea coast was attacked by two drones on Friday, sustaining damage, the Caspian Pipeline Union said.

Sources told Reuters that the ship (Nordic Zenith) is chartered by ExxonMobil.

The Caspian Pipeline Union did not specify who was responsible for the incident. Last week saw a sharp escalation in attacks by both Russia and Ukraine on ships in the Black Sea and the Sea of Azov, marking a new phase in a conflict that has thus far been fought primarily on land and in the air.

The Caspian Pipeline Union added in a statement that a fire broke out on board the vessel Nordic Zenith, but it was later extinguished. It explained that its vessels were nearby and evacuated 13 crew members, while nine others chose to remain on board.

The union said on its Telegram channel, "The tanker has been removed from the loading schedule and is no longer eligible for berthing or loading operations at the Caspian Pipeline Union port."

The Caspian Sea pipeline is 1,510 kilometers long and connects the oil fields of Kazakhstan to the Russian port of Novorossiysk on the Black Sea. Oil loaded in Novorossiysk is then transported by tankers to global markets.

It handles approximately 80 percent of Kazakhstan's oil exports. Its operations were disrupted at various stages of the war due to Ukrainian attacks on pumping stations in Russia, as well as drone strikes on its loading terminal near Novorossiysk.