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Riots broke out in Zambia’s capital as residents protested against incidents of criminals attacking civilians’ houses with gas, prompting the U.S. to issue a security alert.

Unrest that began in the northern Copperbelt province in January reached Lusaka this week, and mobs killed at least three people in the city Thursday, the Zambia Police Service said in a statement.

Police are investigating “incidences of malicious administering of chemical substance on innocent citizens by criminals” and have arrested a number of suspects, it said.

“Rumors of ritualistic killings and residential gassings have led to incidents of civil unrest and vigilante justice in multiple provinces,” the U.S. Overseas Security Advisory Council said in a statement on its website. “Citizen groups are targeting individuals suspected of being involved in the rituals, gassings, or any other criminal activity.”

To contact the reporters on this story: Matthew Hill in Maputo at mhill58@bloomberg.net;Taonga Clifford Mitimingi in Lusaka at tmitimingi@bloomberg.net

To contact the editors responsible for this story: Gordon Bell at gbell16@bloomberg.net, Andre Janse van Vuuren, Yinka Ibukun

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