A group of 15 middle school pupils have been put in criminal detention in Beijing on suspicion of carrying out a series of muggings in early December in the Sanlitun area, a popular commercial district in the capital's downtown area.

Police said the gang operated late at night and targeted multiple victims in the district, which is known for its bars and shopping centers.

All of the suspects study at a nearby middle school, with the youngest aged 13, police said.

Police refused to release detailed information regarding the students as they are minors, but said that with the gang busted, safety has been restored in the area. No school in the area had claimed the students as of Tuesday afternoon.

One of the suspects, surnamed Zhai, said they had spent the money from the robberies in bars and karaoke venues nearby. He said that he was too ashamed to ask his parents for pocket money so he agreed to join the gang.

Police used closed-circuit television footage to track down the gang members, who are accused of threatening their victims with knives and other weapons.

They allegedly worked in small groups, wearing masks and changing outfits frequently to hinder police investigations.

It is not known how many people fell victim to the gang, but a man surnamed Jin was recently interviewed by Beijing Morning Post.

"I was walking along when two teenagers came up to me, said they were hurt and asked me for money," Jin was quoted as saying.

"I tried to ignore them, but they suddenly took out a knife and told me to 'behave' - I was too frightened to fight back."

Jin said the teens took all his cash in addition to taking money from his digital wallet and forcing him to withdraw more cash from an ATM. In total, they stole more than 2,100 yuan ($300) along with his cellphone, he said.

Another victim suffered a nonfatal knife cut for failing to hand over any money, police said.

The gang was busted after police noticed a suspect who resembled one of the robbers from the video footage during a nightly patrol on Dec 9. He later admitted that he was scouting for new victims and led officers to his alleged accomplices, who were subsequently arrested at their homes.

Police said that the tools used in the muggings, such as electric prods, were stored at the suspects' homes, and their parents had failed to notice them.