An angry lynch mob beat a 16-year-old to death and strung him up by the feet from traffic lights in central Baghdad today after accusing the teenager of shooting anti-government protesters.

Dozens of people pointed their mobile phones at the body dangling high above them in a city centre square after he was dragged across the street.

The violence underscored the growing fears and suspicions swirling around the eight-week-old protest movement, which engulfed Iraq on October 1 when thousands took to the streets to decry government corruption, poor services and scarcity of jobs. 

The bloodshed began when the young gunman opened fire in Baghdad's Wathba Square, killing two shop owners and four protesters.

Security officials said the teenager was wanted by police on drug-related charges and was running from security forces at the time. An enraged mob beat the young man to death, security and health officials said.  

The corpse was later removed and taken to a forensic morgue, witnesses said. The morgue confirmed receiving a body. 

A string of mysterious acts of bloodshed by unknown groups has put anti-government protesters on edge and eroded their faith in the ability of state security forces to protect them.