Russia's southern region of Dagestan held the first of three days of mourning Monday following a rampage by Islamic militants who killed 19 people, most of them police, and attacked houses of worship in apparently coordinated assaults in two cities.

Sunday's violence was the latest that officials blamed on Islamic extremists in the predominantly Muslim region in the North Caucasus, as well as the deadliest in Russia since March, when gunmen opened fire at a concert in suburban Moscow, killing 145 people.