Robberies in downtown Minneapolis jumped by more than 50% this year as groups of mostly teenage boys or young men targeted and beat victims for their cellphones and wallets.

Several videos showed groups surrounding victims, who were often alone, intoxicated or distracted, and attacking them. The phones were sold at automated kiosks for quick cash, according to a Minneapolis Police Department report released Wednesday.

In response, police deployed 36 officers to help stop the robberies. Many of the 16 people arrested were suspects in more than one robbery. After the crackdown, just three robberies were reported in the first week of June.

The robberies have primarily occurred in a grid between Hennepin Avenue and 3rd Avenue, and between 3rd Street and 6th Street. One video showed a pack of robbers near Target Field plaza kicking and hitting a man in the head while he was lying on the ground and then riding a bicycle over him.

Police said 240 robberies were reported in Minneapolis this year as of Aug. 26, up from 156 the same time last year. Twenty-three robberies took place in a single week at the end of August alone.