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.

In the early 2000s, Dagestan saw near-daily attacks on police and other authorities that was blamed on militant extremists. After the emergence of the Islamic State group, many residents of the region joined it in Syria and Iraq.

The violence in Dagestan has abated in recent years, but in a sign that extremist sentiments still run high in the region, mobs rioted at an airport there in October, targeting a flight from Israel. More than 20 people were hurt — none of them Israelis — when hundreds of men, some carrying banners with antisemitic slogans, rushed onto the tarmac, chased passengers and threw stones at police.