By Jonathan Spicer and Jonathan Saul

ISTANBUL, Jan 8 (Reuters) - A Russia-bound oil tanker suffered a drone attack in the Black Sea that prompted it to request Turkish coastguard assistance and divert from its course, according to a notice by Lloyd's List Intelligence and a separate maritime security source on Thursday.

Maritime data specialist Lloyd's List Intelligence said the Palau-flagged Elbus vessel "experienced an unmanned marine-vehicle and drone attack" on Wednesday targeting its engine room, and that no injuries were reported among the 25 crew, nor any pollution. 

The security source described it as a drone attack, based on an assessment. It was unclear who or what was behind the incident.

In late November, shipping insurance rates rose after Ukrainian naval drones hit two Russia-bound tankers in the Black Sea, incidents that prompted Moscow to threaten retaliation and Ankara to urge calm. Another vessel, Russian-flagged, said in early December that it too was attacked in the sea, but Kyiv denied any role in that incident. 

The Security Service of Ukraine did not respond when asked about the incident involving Elbus. 

Turkey's transport ministry was not immediately available to comment. The Russian embassy in Ankara was not immediately available to comment. 

The Black Sea is crucial for grain, oil and oil products shipping and its waters are shared by Turkey, Russia, Ukraine, Bulgaria, Georgia and Romania. 

The vessel was headed on Wednesday to the Russian port of Novorossiysk from Singapore, the Lloyd's notice said.

Marinetraffic data showed the Elbus had settled a few kilometres off the northern Turkish port of Inebolu on Thursday, after having diverted from its earlier eastward course across the Black Sea. 

It dropped anchor at Inebolu anchorage under its own power, Lloyd's said. 

Calls to the Inebolu harbour master did not get through. 

(Reporting by Jonathan Spicer in Istanbul and Jonathan Saul in London; Additional reporting by Tom Balmforth; Editing by Alex Richardson and Alison Williams)