Gunmen on Sunday attacked synagogues and churches in Russia's North Caucasus region of Dagestan, killing a priest, six police officers, and a member of the national guard, security officials said.
The attacks took place in Dagestan's largest city of Makhachkala and in the coastal city of Derbent, where gunfights were ongoing.
Russia's Investigative Committee said it had opened criminal probes over "acts of terror", while the hunt for the gunmen was ongoing.
Witnesses could hear shooting near a church in Makhachkala while shootouts were continuing in Derbent, the TASS state news agency reported. Dagestan's interior ministry said it had killed two of the gunmen in Makhachkala.
Sunday is a religious holiday in the Russian Orthodox Church called Pentecost Sunday. Dagestan is a largely Muslim region of Russia, neighbouring Chechnya.
"This evening in the cities of Derbent and Makhachkala armed attacks were carried out on two Orthodox churches, a synagogue and a police check-point," said the National Antiterrorism Committee in a statement to RIA Novosti news agency.
"As a result of the terrorist attacks, according to preliminary information, a priest from the Russian Orthodox Church and police officers were killed."
In all, six police officers had been killed and another 12 wounded in the attacks, the spokeswoman for Dagestan's interior ministry, Gayana Gariyeva, told RIA Novosti.
Russia's National Guard said one of its officers had been killed in Derbent and several others wounded.
A 66-year-old priest was killed in Derbent, the press secretary of Dagestan's interior ministry, Gariyeva told the agency.
- Synagogues on fire -
Dagestan's RGVK broadcaster named the priest as Nikolai Kotelnikov, saying he had served more than 40 years in Derbent.
"The synagogue in Derbent is on fire," the chairman of the public council of Russia's Federation of Jewish Communities, Boruch Gorin wrote on Telegram.
"It has not been possible to extinguish the fire. Two are killed: a policeman and a security guard".
He added: "The synagogue in Makhachkala has also been set on fire and burnt down."
Gorin wrote that in Derbent, firefighters had been told to leave the burning synagogue because of the risk that "terrorists remained inside".
He added: "There is shooting in the streets around the synagogue".
The leader of Dagestan, Sergei Melikov, wrote on Telegram: "This evening in Derbent and Makhachkala unknown (attackers) made attempts to destabilise the situation in society.
"They were confronted by Dagestani police officers."
Russia's FSB security service in April said it had arrested four people in Dagestan on suspicion of plotting a deadly attack on Moscow's Crocus City Hall concert venue in March, which was claimed by Islamic State.
Militants from Dagestan are known to have travelled to join the Islamic State group in Syria.
In 2015, the group declared it had established a "franchise" in the North Caucasus.
Dagestan lies east of Chechnya where Russian authorities battled separatists in two brutal wars, first in 1994-1996 and then in 1999-2000.
After the defeat of Chechen insurgents, Russian authorities have been locked in a simmering conflict with Islamist militants from across the North Caucasus that has killed scores of civilians and police.