It is not yet clear who was behind the attack

The deputy mufti of Dagestan's central mosque, Kurbanmagomed Ramazanov, and his brother Abdulla were killed.

The explosion happened late on Thursday in the republic's capital, Makhachkala. A third man in the car was injured.

Dagestan lies next to volatile Chechnya in the North Caucasus and is the scene of frequent attacks by criminals or Islamist militants.