Jewish groups have protested after it emerged that Russian authorities will investigate an antisemitic theory that the killing in 1918 of Tsar Nicholas II was a 'ritual murder' following comments by a bishop close to the president, Vladimir Putin.

The term 'ritual murder' has in the past referred to a theory that the Tsar was the victim of a Jewish conspiracy.

Bishop Tikhon Shevkunov, who is leading a Russian Orthodox Church commission investigating the execution of the Romanov family by firing squad, said at a conference on Monday that many members of the commission believe that it was a ritual murder that held special significance for the Bolshevik commander Yakov Yurovsky, who was of Jewish heritage, and his men. Russia's investigative committee said it would look into the claim by Shevkunov, who is reported to be Putin's confessor.

Jewish groups reacted to the announcement with outrage. A spokesman for the federation of Jewish communities, Rabbi Boruch Gorin, told the Interfax news agency that the ritual murder investigation was a 'shocking' example of 'medieval ignorance'. The rabbi pointed out that the myth of Jews ritually killing people to extract their blood for matzo bread has featured in antisemitic propaganda for many decades.

The controversy came ahead of Putin taking part for the first time today in the Church's annual bishops council.

The head of the Russian Orthodox Church, Patriarch Kirill, told the conference he had 'hard questions' about the tsarist murder investigation, which they re-opened in 2015, and called on the authorities not to rush it.

The Yekaterinburg news agency Ura.ru quoted a source close to the Church leadership as saying that the Patriarch feared that the ritual murder allegations could 'provoke uncontrollable outbursts of ultranationalism'.

Kirill also said that the Russian Orthodox Church had not yet taken a position on the continued analysis of the Romanov family's remains.

The Church has not recognised the remains of Nicholas, Alexandra and three children interred in St Petersburg cathedral in 1998, nor the remains of his two other children found in 2007, despite DNA testing showing their identity.