A Russian warship has sunk after colliding with a freighter off the coast of Istanbul in the Black Sea, according to Turkey's coastal safety authority.

The Turkish coastguard said all 78 personnel in the Russian intelligence vessel named Liman were rescued on Thursday.

"There are no victims among the crew," Russia's defence ministry said in comments carried by the country's Interfax news agency.

Liman "sustained a hull breach due to a collision" with the ship Ashot-7, 40km northwest of the Bosphorus Strait, according to Russia's defence ministry.

It also said that Ashot-7 "didn't get significant damage and continues to move on its route".

The Russian military said it was trying to identify the owner of the Ashot-7 ship.

Turkey's coastal safety authority said the ship sank after colliding with a Togo-flagged livestock vessel.

Turkish officials did not give any details on the ship, or the condition of its crew.

GAC, a Turkish shipping agency, said separately that the collision was caused by fog and low visibility.

Turkish Prime Minister Binali Yildirim called his Russian counterpart Dmitry Medvedev to express his sadness over the collision, Turkish prime ministry sources said on Thursday.

Reconnaissance ship

The Liman is a former research vessel that the Russian navy has retro-fitted into a reconnaissance ship.

Military sources told Russian media in February that it would be observing NATO's Sea Shield exercise in the Black Sea.

Turkey's Bosphorus Strait, which cuts through Istanbul, is one of the world's most important waterways for transit of oil and grains. The waterway connects the Black Sea to the Mediterranean.