Suspected Chlorine Gas Attack Hits Rebel-Held Aleppo Area

— -- Government forces dropped three barrel bombs laced with chlorine gas on a rebel-held area of the besieged city of Aleppo in Syria on Tuesday, a medical group says, resulting in at least one death and 150 injuries.

Multiple victims suffered from chlorine gas inhalation, including children and women, the Syrian American Medical Society (SAMS) said in a statement. A hospital in eastern Aleppo supported by SAMS told the group it received 36 victims of the attack, while another hospital told the group it had treated 71 victims, including 37 children and 10 women with symptoms consistent with chlorine gas exposure.

"The use chemical weapons is a war crime. This is now the 167th time that chemical weapons have been used in Syria over the past five years," said Dr. Ahmad Tarakji, SAMS President in a statement. "We demand that the UN Security Council takes this seriously... This can not be the new normal in Syria.”

Among the victims, 10 were critically injured, including a pregnant woman in her last trimester, the group said.

Back in 2012, President Obama issued the Syrian government a warning, saying that use of chemical weapons constituted a "red line."

“We have been very clear to the Assad regime," Obama said, "but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus.”

A deal struck with Russia for international inspectors to remove chemical weapons stockpiles from the country helped the Syrian government avoid any U.S. action, but international pressure has mounted again recently as evidence builds of its continuing use of the weapons.

Amnesty International reported the use of chemical weapons by government forces on at least three occasions during a two week period in August. This included a chlorine gas attack that Amnesty says killed four and injured 60 people, 40 of whom were children.

Also last month, the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) confirmed suspicion of chemical weapons use in Syria in 2014 and 2015.

This led the White House to issue a statement blaming the government and calling for it to stop to the use of chemical warfare.

“It is now impossible to deny that the Syrian regime has repeatedly used industrial chlorine as a weapon against its own people in violation of the Chemical Weapons Convention and U.N. Security Council Resolution 2118,” White House National Security Council spokesman Ned Price wrote in a statement. “We condemn in the strongest possible terms the Assad regime's use of chlorine against its own people.”

In an around the city of Aleppo, an estimated 2 million people are now living without regular access to electricity and water, according to United Nations estimates. An estimated 250,000 to 275,000 people live in rebel-held areas that have come under intense airstrikes, artillery bombardment and the suspected chemical attacks.

The overall death toll in the conflict is approaching 500,000, according to a recent study. Intense fighting recently displaced 100,000 people around the city of Hama in just eight days, the UN said.

ABC News's Jon Parkinson contributed to this report.