Rio drug traffickers are operating makeshift medical clinics in the slums they control so wounded gang members don't have to risk arrest by seeking treatment at hospitals, police said Thursday.

"It's the first time we've found clinics like this," a civil police spokesman said Thursday. "We can't say how long they've been used — we assume for some time." He spoke on condition of anonymity, per department rules.

Officers discovered the first clinic Wednesday in the Manguinhos slum in northern Rio. Inside a two-room shack, police found surgical scissors stained with blood; morphine, anesthesia, antibiotics and other medicines; medical equipment such as IVs and X-rays.

Police found bandages with fresh blood on them and surmised that a gunman wounded in a shootout with officers sought treatment at the clinic just minutes before it was discovered.

Police then went looking for other rudimentary facilities — and quickly located one in the nearby Jacarezinho slum, stocked with similar medical supplies.

Police chief Allan Turnowski said an unspecified number of doctors and nurses who worked in the clinics have since been arrested.

"They were making a lot of money" by treating drug gang members, Turnowski said.

Rio's sprawling slums are the site of frequent, bloody shootouts between police and the gangs that dominate the neighborhoods — with innocents often caught in the crossfire. A United Nations report last year found that police kill an average of three people a day in the city.

Wounded drug traffickers know that if they seek treatment in a regular hospital, they risk being handed over to authorities, Turnowski added. "So they've made the investment of setting up these facilities where they can get proper treatment inside of their slum and avoid arrest."

Police have previously arrested doctors who traveled into the slums to treat drug gang leaders, the spokesman said.