Khura-Magomed Ramazanov, a deputy chief mufti at the central mosque in the provincial capital, Makhachkala, died when a radio-controlled roadside bomb turned his vehicle into a fireball, regional emergency agency spokesman Sergei Petrov said.
Ramazanov's driver was also killed in the attack, but his bodyguard survived it with grave injuries and was hospitalized.
Police in Dagestan confirmed that a top cleric and his assistant died when their car burst into flames, but would not immediately give any further details.
Dagestan, a mostly Muslim region east of Chechnya that is home to many ethnic groups, has been plagued by shootings, bombings and other violence, including regular attacks on top officials and police. Some of the violence was linked to Islamic extremists with links to Chechen rebels and some was rooted in turf battles between local criminal clans.