Attacks on churches and synagogues in Russia's Dagestan region killed 15 police officers and four civilians, officials said on Monday, stoking fears over Islamist violence in the historically restive North Caucasus.
Sunday's attacks come just three months after Islamic State (IS) group fighters killed more than 140 in a Moscow concert hall, the deadliest attack on Russia for almost 20 years.
Moscow said on Monday it had concluded an "anti-terrorist operation" and killed five of the assailants behind the coordinated attacks in the cities of Makhachkala and Derbent.
The incidents also had echoes of the kind of insurgent violence that marred the North Caucasus during the 1990s and 2000s but the Kremlin on Monday dismissed fears of a renewed wave of attacks.
Russia has been a target for attacks in recent years by IS, which opposes Moscow's military support for Syrian leader Bashar al-Assad and claims to have set-up a "franchise" in Russia's North Caucasus.
"According to preliminary data, 15 law enforcement officers were killed, as well as four civilians, including an Orthodox priest," Russia's Investigative Committee, which probes major crimes, said on Monday.
Five assailants had been "liquidated", it said.
It was unclear how many had been involved in the attack.
Russian Orthodox archpriest Nikolai Kotelnikov was killed in his church in Derbent, a historic city on the coast of the Caspian Sea.
The National Antiterrorism Committee, which responds to mass attacks and is tasked with foiling terror plots, said it had wrapped up a rapid response operation at 08:15 am (0515 GMT) on Monday.
In the 1990s and 2000s, separatist and militant groups waged guerilla-style campaigns against Russian authorities in the mountainous North Caucasus following the break-up of the Soviet Union.
Moscow fought two wars for control of the neighbouring Chechnya region and President Vladimir Putin touted his success in quashing the insurgency at the start of his presidency.
Asked whether Moscow feared a possible return such violence, Kremlin spokesman Dmitry Peskov said: "No. Now there is a different Russia. Society is consolidated and such terrorist manifestations are not supported by society in Russia or in Dagestan."
Russia's Investigative Committee said it had launched criminal probes over "acts of terror", while Dagestan Governor Sergei Melikov called the attacks an attempt to "destabilise" his region.
"We know who is behind these terrorist attacks and what objective they are pursuing," he added, without providing specific details but making references to the conflict in Ukraine.
"We must understand that war comes to our homes too. We felt it but today we face it," he said.
After the deadly attack on Moscow's Crocus City Hall in March, Putin initially said Kyiv had a hand in planning the assault.
This was despite no evidence or the fact that an IS affiliate claimed responsibility for the attack on multiple occasions.
In a video message posted on social media on Monday, Melikov said authorities were continuing to hunt for members of "sleeper cells" who had prepared the attacks, including with assistance from abroad.
Patriarch Kirill, head of the Russian Orthodox Church and a fervent supporter of the Kremlin, said the "enemy" was seeking to destroy "inter-religious peace" in Russia, without naming who he believed was responsible.
Two Orthodox churches, two synagogues and a police checkpoint were attacked, according to officials and the Russian Jewish Congress.
Melikov visited a church and synagogue in Derbent on Monday.
He posted videos showing a pool of blood in the church and the charred interior of the synagogue, completely burned out after assailants threw Molotov cocktails at the building.
Sunday was a religious holiday, Pentecost Sunday, in the Russian Orthodox Church.
Russian authorities repeatedly announce successful "anti-terrorist operations" targeting alleged IS fighters from the North Caucasus.
The FSB security service in April said it had arrested four people in Dagestan on suspicion of plotting the deadly attack on Moscow's Crocus City Hall concert venue in March, which was claimed by IS.
Tensions are running high in the Muslim-majority region since the start of the war in Gaza in October last year.
In October an angry crowd stormed the local airport when reports circulated on social media that a plane was arriving from Israel.
