A marine drone struck a crude oil tanker that had departed Russia, causing an explosion in the Black Sea near Istanbul's Bosphorus strait on Thursday, Turkey's transportation minister said.

The incident, one of several in recent months involving Western-sanctioned vessels heading to or from Russian ports, occurred in the early hours, minister Abdulkadir Uraloglu told broadcaster Kanal 24.

All 27 crew were safe, he said, adding that the coastguard had been dispatched to the vessel, the Altura, which was about 18 nautical miles (33 km) from the Bosphorus, a key commodities-shipping channel linking the Black Sea with the Marmara and the Mediterranean.

The attack, just outside Turkish territorial waters, likely aimed to disable the engine room in the Sierra Leone-flagged vessel that was carrying Russian oil, Uraloglu said.

Ship-tracking and Refinitiv AIS data showed the vessel had left Russia's port of Novorossiysk with about 1 million barrels of crude oil and appeared almost fully laden.

The ship is sanctioned by the European Union and Britain. The Black Sea is shared by Russia and Ukraine, which have been at war for more than four years, as well as other states.

Turkey's defence ministry said on Thursday it was closely monitoring risks posed in the Black Sea by drones, given their extensive use in the Russia-Ukraine war. Risks included drones losing control or mobility, drifting towards the Turkish coast, it said.

"We are talking to our counterparts and conveying necessary warnings to maintain navigational safety in the Black Sea," it said at its weekly briefing without mentioning Thursday's drone attack, and added Turkish naval vessels were patrolling the area to prevent any damage to vessels or civilians.

Late last year, shipping insurance rates rose after Ukrainian naval drones hit Russia-bound tankers in the Black Sea, prompting Moscow to threaten retaliation and NATO-member Turkey to urge calm.

Ankara has warned both Kyiv and Moscow against carrying out such attacks near its territorial waters amid the escalation in the Black Sea earlier, which saw Russian and Turkish vessels hit by drones and Ukrainian ports damaged.

There was no immediate comment from Moscow or Kyiv on Thursday.

The registered owner of the latest ship to be hit is China-based Sea Grace Shipping Ltd and the manager is the Turkey-based Pergamon Denizcilik, according to Refinitiv data.

Reuters could not immediately contact Pergamon.

Broadcaster NTV earlier reported an explosion on the ship's bridge and water entering the engine room, before the crew sought assistance from Turkish authorities.