An Interior Ministry official told CNN Thursday that the toxic yellow-green gas was a main component in Wednesday's bomb attack near a hospital in southwestern Baghdad's Bayaa neighborhood.
Six people were killed and more than 70 were hospitalized with respiratory problems caused by the noxious gas.
On Tuesday a bomb hidden on board a tanker carrying chlorine gas exploded outside a restaurant in Taji, north of Baghdad, killing six people. At least 140 people were either injured by the blast or sickened by the fumes.
A third chlorine bomb attack occurred in late January. According to the U.S. military, a suicide bomber drove a dump truck loaded with a chlorine tank and explosives into an emergency response unit compound in Ramadi.
No one appeared to be hurt from the chlorine gas, military said, but 16 people were killed in the blast.
The use of gas is a chilling echo of deadly strikes employed by the regime of former Iraqi president Saddam Hussein against his enemies both in and outside Iraq.
Among these was a 1988 attack on the northern Iraqi town of Halabja, where according to U.S. State Department accounts, 5,000 people were killed when Iraqi warplanes attacked the town with bombs containing the nerve gases Sarin and VX.
The attacks formed part of the list of crimes against humanity for which Hussein was tried and hanged last year. (Special report: Saddam Hussein Trial)
It is as yet unknown whether the chlorine attacks are the start of a new trend in Iraq, where suicide car bombs and improvised explosives claim a daily death toll.
CNN is attempting to contact the U.S. military for a statement on the two attacks.
According to the U.S. Centers for Disease Control, exposure to chlorine gas can cause difficulty in breathing, coughing, burning in the nose, throat and eyes, nausea and vomiting.
One of the most commonly manufactured chemicals in the United States, chlorine was employed by the military during World War I as a choking agent, the CDC said.
Chlorine, once pressurized and cooled, changes into a liquid that, when released, turns into a rapidly spreading gas, according to the CDC.
As attacks against coalition targets continued, the U.S. military said that one of its helicopters reported to have had a "hard landing" on Wednesday, might have been brought down by enemy fire.
"The indications are now that it was brought down by small-arms fire and RPGs -- rocket-propelled grenades," Maj. Gen. William Caldwell said.
A message posted online by a group called the The Mujahedeen Army claimed responsibility for downing the UH-60 Black Hawk helicopter.
CNN cannot confirm the authenticity of the claim or its source.
A portion of the statement, dated Wednesday, said, "With God's blessing, at 10 o'clock this morning, Sheik Al-Islam bin Taimiya Brigade of the Mujahedeen Army was able to down a Black Hawk helicopter that belongs to the crusader occupying forces in the Taji area, north of Baghdad."
Also Wednesday, British Prime Minister Tony Blair announced plans to draw down the number of British troops in Iraq. Similar announcements were made by leaders in Denmark and Lithuania.
The United States rejected claims that its military coalition was crumbling, insisting the move reflected the relative stability in the southern Iraq regions patrolled by the British.
CNN's Mohammed Tawfeeq contributed to this story.Güncelleme Tarihi: 20 Eylül 2018, 18:16