The group released a comprehensive report accusing the Syrian government of using chemical weapons against insurgents in Homs, Aleppo, Damascus and Idlib in 2012 and 2013.
"Using poisonous gases in different Syrian Territories violated both International Human Rights Law and International Humanitarian Law," the report said.
It included testimony from survivors, eyewitnesses and physicians collected by network team members during field visits to each of the attack sites, the network said.
The group documented the very first incident of chemical weapon use as occurring in Homs on December 23, 2012. Six people died and at least 120 others sustained injuries ranging from paralysis to nausea and vomiting.
The last attack covered by the report occurred in Damascus on June 27, 2013 when government forces used poisonous gas against the Qaboon neighborhood, killing one person and injuring more than 10 others, the human rights group said