Gunmen shot dead an Islamic cleric in the internal Russian republic of North Ossetia, investigators said on Thursday, an attack that suggests militant Islamist violence in Russia's southern Muslim provinces is spreading to nearby regions.

Shootings and bomb attacks on police and officials are a near daily occurrence across much of Russia's restive North Caucasus, but violence in North Ossetia - a mainly Christian region - is unusual.

Gunmen shot dead 34-year-old Ibragim Dudarov, North Ossetia's deputy mufti, many times in the head at point blank range as he was driving late on Wednesday near the provincial capital of Vladikavkaz, the Investigative Committee said in a statement.

The killing - at least the sixth this year of a Muslim religious leader - is likely to inflame tensions between moderate and more radical Muslims.

Moscow is struggling to extinguish an insurgency that stems from its two devastating wars against separatists in Chechnya, just east of Ingushetia and North Ossetia, and has been fuelled by chronic unemployment, police brutality and poverty.

Militants fighting for an Islamic state in the mountainous region have increasingly targeted Muslim leaders who are backed by the Russian authorities.

"This man died for his faith. I think it is linked to his work," North Ossetia's top Islamic official Khadzhimurat Gatsalov told the Interfax news agency.

"Someone doesn't want this kind of Islam in North Ossetia."

Two decades after a territorial dispute erupted into a brief war in 1992, there is also lingering tension between mostly Christian North Ossetia and mostly Muslim Ingushetia, but there was no indication the shooting was linked to that conflict.

On Thursday, the National Anti-Terrorism Committee (NAK) said police had killed three suspected militants in the Kabardino-Balkaria region on Dec. 26.

NAK identified one of those killed as Alim Lampezhev, who has been on Russia's federal wanted list since 2010.