Two top Muslim clerics in the Russian region of Tatarstan were attacked Thursday as they prepared to begin the holy month of Ramadan at sundown. One of the men was killed.

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

The mufti of Tatarstan, Ildus Faizov, was thrown from his car and injured when the vehicle exploded in Kazan, the regional capital, on Thursday. In another part of the city, Faizov's former deputy, Valiulla Yakupov, was shot to death outside his home.

Both men were known for promoting moderate Islamic practices and fighting the spread of radicalism to Tatarstan from the more volatile Caucasus region in southern Russia.