The Russia-backed Syrian military and its allies entered ISIS-held Raqqa, where U.S.-backed forces are battling the jihadis.
Human Rights Watch have condemned the "horrific, long-lasting harm" that the weapon could inflict upon civilians in ISIS territory.
The civilians were escaping the city using a dinghy to cross the Euphrates.
The militant group is reportedly gathering its top chemical weapons experts in the Euphrates River Valley.
Syrian Democratic Forces (SDF) captured the town west of ISIS's de-facto capital.
Ankara has lashed out at Trump administration plans to back Kurdish forces in push for ISIS capital Raqqa.
The U.S.-backed, majority-Kurd Syrian Democratic Forces and the Russia-backed Syrian military are separately threatening ISIS's final major strongholds.
Observers and U.S.-backed forces confirmed the majority of the casualties were civilians.
Russia will not want to be the only great power in warring Syria after ISIS is defeated.
Almost half the total Shia combat fatalities in Syria 2012-2017 were Hezbollah fighters.
The president has not yet articulated his policy toward Assad, the counter-ISIS campaign or Russia.
Will Trump be able to resist the temptation to escalate the war against Assad?
The administration understands Bashar al-Assad's utter subordination to Iran for the sake of Hezbollah.
The fall of the Syrian city could signal the end of ISIS's state-building project.
Terrified residents fled to nearby hills.
Has Donald Trump ordered looser targeting standards in Iraq and Syria that cause more civilian casualties?
A Kurdish and Arab coalition, backed by U.S. special forces, is waging the ground offensive against ISIS.