A synagogue, an Orthodox church and police checkpoints were targeted by gunmen in a coordinated series of attacks in Russia's southernmost Dagestan province on Sunday night. Four civilians, including a priest, and 15 police officers were killed in the attacks, investigators said Monday.

"According to preliminary data, 15 law enforcement officers were killed, as well as four civilians, including an Orthodox priest," Russia's national Investigative Committee said in a statement, adding that five perpetrators were also "liquidated."

The spokeswoman for Dagestan's interior ministry, Gayana Gariyeva, had earlier told the state-run RIA Novosti news agency that a 66-year-old Russian Orthodox priest was among those killed. 

The attacks took place in Dagestan's largest city, Makhachkala, and in the coastal city of Derbent. Russia's National Anti-Terrorist Committee described the attacks, in the predominantly Muslim region with a history of armed militancy, as terrorist acts.

Dagestan's Interior Ministry said a group of armed men shot at a synagogue and a church in the city of Derbent, located on the Caspian Sea. Both the church and the synagogue caught fire, according to state media. Almost simultaneously, reports appeared about an attack on a church and a traffic police post in the Dagestan capital Makhachkala.

The authorities announced a counter-terrorist operation in the region. There was no immediate claim of responsibility for the attacks.

At least some of the attackers initially fled in a car, but it was not immediately clear whether the five slain suspects accounted for all of the attackers or if more were still believed to be on the loose.

Russian officials blame Ukraine, NATO

While was no immediate claim of responsibility, CBS News senior foreign correspondent Charlie D'Agata said the bloodshed came three months after 145 people were killed in an attack claimed by ISIS on a concert hall outside Moscow.

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Russia's predominately Muslim republic of Dagestan has been a hotbed of Islamic extremism for decades, but some officials from the region blamed Ukraine and its backers in the U.S.-led NATO alliance for the carnage over the weekend.

"There is no doubt that these terrorist attacks are in one way or another connected with the intelligence services of Ukraine and NATO countries," Dagestan lawmaker Abdulkhakim Gadzhiyev wrote on Telegram, according to the Associated Press.

Ukrainian officials did not immediately comment on the attacks.

"What happened looks like a vile provocation and an attempt to cause discord," President Ramzan Kadyrov of neighboring Chechnya, an ally of Russian President Vladimir Putin, said, according to The Associated Press.

"We understand who is behind the organization of these terrorist attacks. We understand what the organisers were trying to achieve," declared Dagestan Governor Sergei Melikov in a video statement released Monday, adding without any elaboration: "They had been preparing, including from abroad."

He vowed that further "operational search and investigative measures" would be conducted "until all participants in these sleeper cells are identified." 

Dagestan is a mainly Muslim region in southern Russia bordering Georgia and Azerbaijan. Derbent is home to an ancient Jewish community in the South Caucasus and a UNESCO world heritage site, Reuters reported.

—The Associated Press contributed reporting.

In:
• Terrorism
• Chechnya
• Islam
• Ukraine
• Russia
• Vladimir Putin