By Steve Gutterman

MOSCOW (Reuters) - Russian authorities said they detained four suspects on Friday over attacks that wounded the top Islamic official in the mostly Muslim Tatarstan region, killed his deputy and raised fears of the spread of militancy to Russia's heartland.

The federal Investigative Committee suggested the attacks - in an area previously held up as a model of religious tolerance - were provoked by disputes over faith and money.

Tatarstan's mufti, Ildis Faizov, was hospitalized after three powerful blasts hit his car in Tatarstan's capital, Kazan on Thursday. A little earlier, deputy mufti Valiulla Yakupov was shot dead outside his home.

The attacks evoked the deadly violence that plagues mainly Muslim regions of the North Caucasus, where federal forces have fought rebels in two devastating wars since the 1991 Soviet collapse and militants want to carve out an Islamic state.

Militants in the Caucasus sometimes target mainstream Muslim leaders backed by the authorities. The attacks in Tatarstan - on the Volga River east of Moscow and far from the Caucasus - suggested similar tensions may be deepening there.

"Investigators believe the main motive was the professional activity of the victims, including their ideological differences with opponents," the Investigative Committee said in a statement.

Faizov had taken "a tough position toward organizations that preach radical forms of Islam" since his election in April 2011, it said.

"In addition, he took control of the movement of financial resources of the organization Ideal-Hadzh, which sent Muslims to Mecca, and on this basis a conflict occurred between the mufti and the leader of this organization, which threatened him." Continued...