BAGHDAD — Iraqi security forces stepped up patrols Saturday in the southern city of Basra, a strategically important oil port on the border with Iran where longstanding protests about quality of life have escalated into days of rioting and violence.

The predominantly Shiite city is among the poorest areas of Iraq, despite the huge nearby oil reserves that drive the national economy. Although Basra has escaped the terrorist violence that has racked the country for years, its population has struggled with its own set of problems: high unemployment, crumbling infrastructure and rampant organized crime groups with leaders linked to powerful Shiite militias.

The city sent tens of thousands of its young men to northern Iraq in 2014 to fight against the Islamic State. Now, as many of them have returned from battle to these same old problems, their anger has intensified, driven by a sense of frustration that their sacrifices at war haven’t come with tangible socioeconomic gains.

Since June, Basra residents have organized some of the largest street protests in years, demanding clean water, jobs and better infrastructure in a city that hosts a world-class stadium but where many residents live in crumbling dirt-brick houses in shantytowns.