Gitinmagomed Abdulgapurov's death early Friday was the fifth killing of a Muslim cleric in the restive province in the past two years.
Daghestani authorities say a handmade explosive device hidden in a heap of garbage and operated by a mobile phone killed Abdulgapurov and his guard instantly.
At the time of his death, Abdulgapurov, who was known for criticizing radical Islamists, had been placed under police protection after receiving death threats.
Daghestan and other areas of the Russian North Caucasus have seen frequent violence in the regional conflict between security forces and suspected Islamist militants.
Daghestani President Magomedsalam Magomedov on March 22 announced that police in the Russian Caucasus republic would be reinforced "because the security situation arouses certain concern."
Magomedov, however, denied rumors that some 25,000 Russian Interior Ministry troops would be arriving.