Ivory Coast taxi driver Mamadou Bamba had finished his shift and was walking home around midnight when a dozen children accosted him on the street and demanded his money. When he hesitated, the thieves pulled out small knives and stabbed him eight times before making off with fares totaling more than $100.

The attack made Bamba the latest victim of the "microbes," roving bands of kids as young as 12 whose violent robberies the past few weeks have raised alarm over crime in working-class neighborhoods of Abidjan, Ivory Coast's largest city. Though not a new phenomenon, tabloid coverage of the "microbes" — the French word for germs — combined with fears they are spreading to new parts of town have residents complaining that the government has failed to keep them safe.

Some Ivorians have even changed their Facebook profile photos to a black screen with white letters spelling out an urgent plea: "Save us from the microbes."

President Alassane Ouattara's government has described the "microbes" as children traumatized by Ivory Coast's postelection crisis of 2010-11, which claimed more than 3,000 lives after ex-President Laurent Gbagbo refused to accept defeat. Interior Minister Hamed Bakayoko has pointed to treatment centers established to get them off the streets.

In the past two years, though, the problem seems only to have gotten worse.

"The phenomenon has expanded because no one was listening to the cries of distress of the suffering population," said Pierre Kouame Adjoumani, president of the Ivorian Human Rights League. "The children have transformed themselves into veritable gangs."

Victims of the latest attacks blame the government for abandoning them.

"It's deplorable," said Laura Adeline, a 57-year-old fruit vendor in Yopougon district who fled as her stand was ransacked last week. "Nothing here is guarded. There is no security."

A separate incident earlier this month on the same street where Adeline works brought public anger to a new peak. Larissa Claude Abony, a 23-year-old student, was waiting for a bus before dawn on Aug. 12 when she was stabbed to death in an attack neighbors quickly blamed on the "microbes," though no witnesses have come forward. In the days after her body was found, videos circulating on social media showed residents of the neighborhood chasing suspected "microbes" through the streets with knives and machetes.

"It's self-defense now," said Pamela Komoe, 32, who lives above the bus stop where Abony was attacked and said she heard the student's cries for help in the moments before she died. "If we have no one to defend us, we are obligated to defend ourselves."

Some 300 extra police officers were deployed to Yopougon late last week, said Joseph Kouame Yao, the top police official responsible for Abidjan. But in a local radio interview Yao also questioned whether the "microbes" had much of a presence in the district.

Many Yopougon residents said that if the authorities do not respond, ordinary civilians will take matters into their own hands and even kill the "microbes" if necessary.

Human rights leader Adjoumani urged the public to refrain from vigilante violence. He said it is likely the children are unable to attend school, making them easy prey for adults looking to use them to commit crimes. And he called on authorities to focus on alleviating poverty, which he said was the root cause of the problem.

"No one has the right to kill another person for a crime," he said. "These are children coming from poor families who are engaging in theft in order to provide for their relatives."