A female suicide bomber posing as a Muslim pilgrim killed a leading Islamic scholar and at least five others on Tuesday in Russia's restive Muslim region of Dagestan.
The attack was reported just as President Vladimir Putin began delivering a keynote address devoted to an assassination attempt last month against another top moderate cleric in a different republic that killed his former deputy.
The rapid succession of assassination is likely to set off alarms in the Kremlin amid signs that its strategy of winning over the North Caucasus by backing less radical forces is coming under direct militant attack.
Dagestan's interior ministry said Tuesday's attack claimed the life of one of the Caspian Sea region's most respected religious leaders who had worked for most of his life against the rise of radical Islam.
Its official statement said a woman 'posing as a pilgrim' walked into the home of Sheikh Said Afandi and detonated a suicide belt.
The federal Investigative Committee said Afandi was one of seven people instantly killed by the bomber.
"The woman's identity is now being established," the Investigative Committee said in its own statement.
The scholar is a Dagestani native who was born in 1937 and had studied Islam in the Soviet era before establishing warm relations with the current Russian authorities.
The latest high-profile slaying occurred just weeks after militants claimed a car bombing and shooting in the main Muslim region of Tatarstan - held up as an example of religious tolerance - that targeted its own religious leaders.
The Tatarstan clerics and Afandi were all Sufis who promoted a form of cooperation with the authorities, having strongly backed Putin before.
The first attack prompted the Russian strongman to call an emergency security meeting just two months into his new term as president and then deliver a series of big speeches preaching inter-ethnic peace.
Putin flew to Tatarstan on Tuesday to deliver some more prepared remarks on the dangers of separatist sentiment and the strength of a unified Russia.
But his message aired on national television just as the first reports of the Dagestan blast filtered in through Russian news agencies.
Putin never referred to Dagestan directly while vowing that 'you cannot defeat the united, multi-ethnic and powerful Russian people'.
"We have truth and justice on our side - and millions of people," he said in the emotional appeal.
"And these are people who are not afraid, who cannot be frightened, and who know the value of peace."
There was no immediate claim of responsibility for the attack.
But it came just days after Russia's most feared Islamist commander - the long-wanted warlord Doku Umarov of the Caucasus Emirate group - appointed two new top deputies in charge of Dagestan.
One was a new field commander directly responsible for orchestrating attacks against both Russian state and security targets as well as those who promote more tolerant Muslim religious views.
Russian authorities meanwhile said they suspected that a border guard who killed seven of his fellow servicemen at a Dagestani outpost earlier in the day before being shot dead himself may have had ties to the militant movement.
"According to preliminary information, the border guard who opened fire on his colleagues had been recruited by the bandits," Interfax quoted a local security source as saying.
The unnamed soldier shot dead two soldiers guarding the barracks of an outpost near the coastal Caspian Sea city of Derbent before entering the building and killing five more people.