Authorities will investigate an anti-semitic theory that the 1918 killing of Tsar Nicholas II was a “ritual murder” following comments by a bishop close to Vladimir Putin.

Bishop Tikhon Shevkunov, who is heading a Russian Orthodox Church commission investigating the execution of the Romanov family by firing squad in Yekaterinburg, said at a conference on Monday that many members of the commission believe it was a ritual murder that held special significance for Bolshevik commander Yakov Yurovsky and his men.

“Ritual murder” has in the past referred to a theory that the last emperor was the victim of a Jewish conspiracy, as Mr Yurovsky was of Jewish heritage.

Russia's investigative committee said it would look into the claim by Mr Shevkunov, who is reputed to be Mr Putin's confessor.

The announcement drew an outcry from Jewish groups.