(Bloomberg) -- A deadly attack by gunmen in the majority Muslim region of Dagestan just months after the assault on a Moscow concert hall is raising the spectre that Russia may be facing a wave of violence by religious extremists.

Security services said that terrorists were behind Sunday’s attacks that targeted two churches and a synagogue in the often violence-wracked region in southern Russia. At least 15 police officers and four civilians, including a priest, were killed, Russia’s Investigative Committee said Monday on Telegram.

Among six militants who were killed, three were sons and a nephew of a local official that the ruling United Russia party later expelled, according to the Interfax news service. Investigators are trying to establish who was responsible for organizing the attacks. 

A close ally of President Vladimir Putin, the speaker of Russia’s upper house of parliament, Valentina Matviyenko, alleged Russia had information of “confirmed foreign funding” for the attack. Law enforcement agencies “will clear out extremist cells in the shortest possible time, complete investigative actions and reliably establish” where and to whom threads lead, she said. 

The assault came three months after gunmen carried out the worst atrocity in Moscow for two decades, killing more than 140 people in a March 22 attack on the Crocus City Hall concert venue. Russia initially pointed the finger at Ukraine for the assault that was claimed by Islamic State. Security services eventually acknowledged that Islamic State’s branch in Afghanistan was behind the Moscow attack, the biggest single loss of life in the capital since Chechen separatists took hostages in 2002 at the Nord-Ost theater.

The Islamic State’s Afghan subsidiary issued a statement on its Russian-language Al-Azaim channel praising the militant assault in Dagestan, which it said was carried out “by our brothers from the Caucasus,” according to the Washington-based Institute for the Study of War.

The latest attacks stood out for their coordination and scale. Russian Telegram channels posted several videos of men wearing black T-shirts shooting at police cars. Another video depicted a fire destroying a synagogue.

“There’s a huge problem with Islamic extremism in Russia, which is spreading,” said Sergei Markov, a political consultant close to the Kremlin. “Islamic State and other groups are active.”

That a local official’s relatives were among the militants “shows that radical Islam has gone deep into society and penetrated the elite,” Markov said.

Kremlin spokesman Dmitry Peskov dismissed the idea of a wave of extremist violence, saying “now Russia is different,” according to Interfax. 

Islamist groups have targeted Russia in the past, citing what they call anti-Muslim policies by the Kremlin. 

In October, a mob encircled a flight from Israel at the airport in Dagestan’s regional capital of Makhachkala in protest at Israel’s war against the militant group Hamas in Gaza. It took hours to restore order. 

A Dagestani lawmaker from the ruling pro-Kremlin party, Abdulkhakim Gadzhiev, accused the North Atlantic Treaty Organization states and Ukraine of plotting the latest attack.

Dmitry Rogozin, a senator in Russia’s upper house of parliament who has served as deputy prime minister, warned that ascribing every homegrown terrorist act to NATO and Ukraine “will cause big problems for us,” in a post on his Telegram account.

Russia’s insistence on blaming radical Islamic violence on Ukraine and its allies is making it impossible to counter it effectively, said Gregory Shvedov, an expert on southern Russia’s mainly Muslim regions.

“The biggest problem now is they are refusing to acknowledge the threat,” Shvedov, who’s editor-in-chief of Caucasian Knot, said by phone. “These attacks bear all the hallmarks of Islamic State and there are large numbers of sympathizers who operate beneath the surface.”

(Updates with Islamic State statement in sixth paragraph)

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