Human Rights Watch, which monitors abuses around the world, said in the report published on Monday that Syrian government forces had dropped chlorine bombs "in residential areas in Aleppo on at least eight occasions" late past year.
On Monday, Human Rights Watch released a report documenting chemical weapon use in Aleppo. HRW emphasized that the pattern of the attacks indicated careful coordination by the military and clearly ruled-out rogue operations by a few.
Around 200 people were also injured by the toxic gases used in the attacks, the report said, basing its findings on witness interviews, pictures and video footage obtained.
Human Rights Watch said the attacks were carried out between November 17 and December 13 - two days before President Bashar Assad's forces took control of eastern Aleppo in a humiliating defeat for opposition fighters trying to oust the Syrian leader.
The attack killed nine people and wounded hundreds of others.More news: JC Penney Company Inc (NYSE:JCP) & People's United Financial, Inc
Chlorine use as a weapon is banned under the Chemical Weapons Convention, which Syria joined in 2013 under pressure from Russian Federation. The use of the gas is well short of the sort of chemical weapons Syria had in its arsenal before signing the ban, but still illegal because of the danger of civilian exposure.
But Russia, Syria's closest ally, has repeatedly questioned investigators' conclusions linking chemical weapons use to the Assad regime.
Despite lack of conclusive evidence, a number of countries, in particular the United Kingdom, France, and the United States, blamed the Syrian government for the chemical attacks.
It also urged the 192 parties to the Chemical Weapons Convention to address Syria's alleged violations of the treaty.