Five people were shot dead after a gunman opened fire on worshippers leaving church in Russia's southern province of Dagestan.
Another five people were injured in the attack on the village of Kizlyar in the Muslim-majority republic of Dagestan, local news agencies reported.
The small republic in the Caucasus mountains borders Chechnya, where Moscow has led two wars against separatists and radical religious groups since the 1991 Soviet collapse.
It is one of the poorest and most unstable regions in Russia and has seen a large number of people join Islamic State.
The Russian RBK daily quoted an Orthodox priest saying the attacker opened fire on churchgoers following an afternoon service. 'We had finished the mass and were beginning to leave the church. A bearded man ran towards the church shouting "Allahu Akbar" and killed four people,' Father Pavel said. 'He was carrying a rifle and a knife.'
A fifth person later died in hospital.
Russian news agencies said the attack occurred as churchgoers celebrated Maslenitsa, a Christian holiday marking the last day before Lent according to the eastern Orthodox calendar. It is also exactly a month before Russia's elections on March 18 which sitting president Vladmir Putin is almost certain to win.
Isis said it had established a affiliate in the North Caucasus in 2015 and has claimed responsibility for a number of attacks on police in Dagestan in the past couple of years involving guns and explosives. Local security forces are battling an Islamist insurgency but attacks on the region's minority Russian Orthodox population are rare.
The assailant was identified as a 22-year-old man local to the region, the TASS news agency said, citing the investigative committee.
He was shot and killed by security services who were on duty nearby, TASS said, adding that a hunting rifle, bullets and a knife were discovered on his person.
Initial reports suggested all five victims were women, TASS said, citing the local branch of the interior ministry.
The injured include two members of local security services and two civilians, also women, the Interfax news agency said.
Additional reporting by Reuters.
