Ravil Gainutdin, chairman of the Muftis' Council of Russia, extended his condolences to the Russian Orthodox Church and the family of the dead priest. The grand mufti called on people not to speculate on possible motives, and reiterated his community’s opposition to “any extreme act or act of terror”.

Patriarch Kirill, head of the Russian Orthodox Church, tried to downplay the incident, urging people not to quickly draw any conclusions against this or that group. He also distanced himself from the 35-year-old dead priest who was a leading figure in the fight against Islamic extremism and ultra-nationalism.

Known as the Russian Salman Rushdie, Fr Sysoyev was shot four times in the Church of Saint Thomas in Moscow. The choirmaster was also wounded during the attack. The murderer entered the church wearing anti-flu masked and a gun with silencer.

Investigators believe that religion might be the main factor in the murder.

A missionary with the zeal of a latter-day crusader, Fr Sysoyev was also a respected theologian.

On his blog and in a recent interview with Komsomolskaia Pravda, he had said that he had received at least ten death threats by e-mail and phone (“They [radical Islamists] want to cut my head off”).

Russia’s security service, the FSB, was aware of the threats.

Given his work, it was easy for Fr Sysoyev to make enemies. Not only was he was involved in evangelisation among immigrants from the Caucasus and Asia, but he was especially known for promoting the idea in books and online that dialogue with Islam was impossible and that women were treated like slaves in the Muslim world.

His enemies included some ultra-nationalist groups and Stalinist diehards. On his blog LiveJournal, he wrote on the anniversary of the Bolshevik revolution earlier this month that Christians should not even sit at the same table with Communists.

There is no clear lead in the investigation yet, but for many he was an “infidel”. His death was in fact met with cheers on Internet forums for radical Islamists, some acknowledging that they had dreamt of knifing him to death personally.

Fr Sysoyev’s funeral took place last Sunday with hundreds attending. Many of those who left the church after the function expressed anger and blamed the Muslim community, the Russian press reported.

The crime continues to resonate across the country and is putting strains on the already fragile relationship between the dominant Orthodox Church and Muslims, who constitute Russia’s second largest religious group and Europe’s largest Muslim community (20 million members).