An angry mob killed a 16-year-old and strung up the corpse by its feet from a traffic pole after the teen shot and killed six people on Thursday, including four anti-government protesters, Iraqi officials said.

Dozens of people pointed their cellphones at the body dangling high above them in a central Baghdad square.

Videos circulating on social media showed the young man being beaten and dragged across the street.

The violence underscored the growing fears and suspicions swirling around the 8-week-old protest movement, which engulfed Iraq on Oct.1 when thousands took to the streets to decry government corruption, poor services and scarcity of jobs.

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.

Last Friday, 25 protesters were killed when gunmen in pickup trucks opened fire in Baghdad’s Khilani Square.

That same week, mysterious knife attacks targeted over a dozen anti-government protesters in Tahrir Square, the hub of the protest movement.

In recent days, abductions and assassinations of high-profile civil activists have stoked paranoia among demonstrators.

Protesters largely blame Iran-backed militias for the attacks and see the violence as a campaign to instill fear and weaken their peaceful movement.

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

Security officials said the teen 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 officials spoke on condition of anonymity in line with regulations. At least eight people were wounded, the officials said.

Influential Shiite cleric Muqtada Al Sadr called those who killed the teen “terrorists” and warned that if they were not identified within 48 hours, he would order his militia to leave the square. Members of Saraya Salam, or Peace Brigades, are deployed in the square to protect protesters. Protesters refer to them as the “blue hats.”

The killing of the teenager was condemned by the wider protest movement in Tahrir Square, which said in a statement that the perpetrators were not part of their peaceful demonstrations.

“We can’t allow the image of our pure revolution to be distorted, so we declare that we are innocent as peaceful demonstrators to what happened this morning in Wathba Square,” the statement said.

Separately, two rockets were fired at a military base near Baghdad airport housing US troops, the 10th such attack since late October, the Iraqi army said on Thursday.

There were no casualties in the overnight attack, which follows one on the same base on Monday which wounded six members of Iraq’s elite US-trained counterterrorism force, two of them critically, the army said.

Washington has expressed mounting concern about the flurry of attacks on US bases and diplomatic missions, several of which it has blamed on Shiite militia groups trained by its foe and rival for influence Tehran.

Security sources have linked at least one attack last week to Kataib Hizbollah, a powerful Shiite faction close to Tehran and blacklisted by Washington.

Iran holds vast sway in Iraq, especially among the more hardline elements of the Hashed Al Shaabi, a paramilitary force largely made up of Shiite militias.

A US defence official said the rocket attacks made the Hashed a bigger security threat to American troops in Iraq than the Daesh militant group which the US has vowed to help Baghdad wipe out.

On Friday, the United States imposed sanctions on three senior Hashed figures.

Tensions between Iran and the US have soared since Washington pulled out of a landmark nuclear agreement with Tehran last year and reimposed crippling sanctions.

Agencies