MOSCOW - Authorities in Russia said Monday they didn't rule out the possibility that Sunday's fatal shooting incident in the country's predominantly Muslim Republic of Dagestan, was a terrorist attack.

The Russian Investigative Committee said it was taking into consideration "various theories" while trying to establish the attacker's motives.

"A terror attack is among possible theories," the TASS news agency cited the committee's spokeswoman Svetlana Petrenko as saying.

On Sunday, a gunman identified as a local resident born in 1995 opened fire at worshipers in an Orthdox church in the city of Kizlyar, killing four women on the scene and wounding five others, including police and National Guard officers. One of the injured, also a woman, later died in hospital.

The assailant was shot dead by security services personnel responding to the incident when he was trying to flee the scene. It was later discovered that the attacker was armed with a hunting rifle and a knife.

The investigative committee said it had launched a criminal investigation into the incident on the grounds of attempted murder and encroachment on the lives of law enforcement officers.

There have been reports that the Islamic State militant group had claimed responsibility for the attack.

At the time of the shooting, churchgoers were celebrating Maslenitsa, a religious holiday marking the last week before Lent, which is the eighth week ahead of the Orthodox Easter.

Located in the North Caucasus region, the Republic of Dagestan borders the Chechen Republic, where the Russian government forces fought two wars against Islamic separatists following the demise of the Soviet Union in 1991. It is also home to a number of radical insurgencies in recent memories.