A Ukrainian naval drone struck a Russian oil tanker in the Kerch Strait off occupied Crimea under the darkness of night.  Kyiv's maritime agency warned that all Russian ports should now be considered a war risk area.<br />''<br />''According to a Ukraine Security Service source, a drone carrying 450 kilogrammes (992 pounds) of TNT struck the 141-metre Russian-flagged ship the Sig outside the Black Sea port of Novorossiysk. According to Russian authorities, the strike left a hole in the engine room of the ship . Russia's Federal Agency for Marine and River Transport said no casualties were reported and that the Sig was not carrying oil when the drone crashed into ship.  In retaliation Russia also dropped guided air bomb at a blood transfusion centre in north-eastern Ukraine.   President  Volodymyr Zelensky has said rescuers were trying to tackle a blaze after the strike on the Kupiansk community in the Kharkiv region last night .Clashes in the black sea region have increased in the recent weeks after Russia abandoned a major UN deal that enabled grain to be safely exported across the area.<br />