Chlorine gas attacks paved the way for Syrian forces as they advanced into rebel-held portions of east Aleppo during the final months of the battle for the city, a new study from Human Rights Watch said Monday.

While forces loyal to Syrian President Bashar al-Assad have used chlorine gas on opposition fighters sporadically since 2014, the frequency of chemical attacks between Nov. 17 and Dec. 13 point to a military strategy to use the banned weapon to force both fighters and civilians from Aleppo, according to the report. Continue reading.