Russian authorities say they have detained four people suspected of killing a top Muslim cleric and wounding another in Tatarstan province.

Moscow-based investigators said they believe the two clerics were targeted for promoting moderate Islamic practices and fighting the spread of radicalism to Tatarstan from the more volatile Caucasus region in southern Russia.

The chief mufti (religious scholar) of Tatarstan, Ildus Faizov, was wounded in a car bomb attack, and his former deputy, Valiulla Yakupov, was shot dead outside his home Thursday in what appeared to be coordinated attacks.

President Vladimir Putin called the attacks “a serious signal” of rising tensions in the region.