Russia is accused of possible war crimes for using white phosphorus on targets in areas populated with civilians – a direct breach of the Geneva Conventions.
White phosphorus, or WP, is a chemical weapon used to illuminate combat areas at night or create smoke screens to cover ground forces.
A highly toxic and flammable substance, WP can burn through skin and bone and has been known to cause long-term problems for vital organs and death in extreme cases of exposure.
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For this reason the incendiary weapon is banned from use in civilian areas under the Geneva Conventions designed to protect non-combatants.
But Russia has been accused of flouting these protocols in its bombing campaign on Syrian rebels and ISIS targets.
According to humanitarian workers and eyewitnesses on the ground, the Russian military has used WP in recent weeks over cities in northwest Syria filled with civilians as it attacks enemies of the Assad regime.
Russia is accused of dropping WP on the ISIS stronghold of Raqqa and the city of Idlib, both full of civilians. One witness told The Times many were left "horrific injuries".
“We knew it was phosphorus because the entire sky lit up and when it settled it set everything on fire,” one witness known only as Ahmed told the newspaper.
Ahmed claimed activists in the area intercepted Russian military radio chatter that allegedly discussed targeting cities more than 50 kilometres from the nearest military targets.
Some activists claim Russia has killed more civilians than military targets while the London-based Syrian Observatory for Human Rights estimates that of the 1,502 people killed in Russian airstrikes, 32 percent were civilians.
The Geneva Conventions have often been flouted in the War on Terror, with the Bush Administration justifying the use of torture and imprisonment of potential terrorists by declaring them "non-enemy combatants" – a term that allowed them to skirt around the framework.
Human Rights Watch accused Israel of war crimes during its assault on Gaza in August last year when it "fired white phosphorus repeatedly over densely populated areas, even when its troops weren't in the area and safer smoke shells were available.
"As a result, civilians needlessly suffered and died".