Video verified by the Washington Post shows shells used in an artillery strike in Gaza exploding with the telltale signs of white phosphorus, a chemical that can cause severe burns on people and can be devastating to a civilian population. The use of the chemical is not banned by conventions of war and it is sometimes used to mark targets for additional artillery or air strikes. The shells reportedly landed in the Gaza City port away from residential areas, but Human Rights Watch warned that using white phosphorus in densely populated Gaza City will inevitably lead to civilian casualties.