Israel has reportedly used white phosphorus near Lebanese cities and towns. What is it?

A piece of alleged white phosphorus still burns at UNRWA's (UN Relief and Works Agency) primary school in Beit Lahia in the northern Gaza Strip on January 24, 2009. Oliver Laban-Mattei/AFP hide caption

Human rights groups and The New York Times say they have documented Israel's use of the chemical white phosphorus over civilian areas in Lebanon. It is a substance that can cause severe burns, respiratory issues and death.

The New York Times reported Saturday that Israel used white phosphorus in the Lebanese town of Nabatieh May 30 by verifying social media videos.

Israel re-started strikes on the Iran-backed militant group Hezbollah in Lebanon shortly after Israel and the U.S. jointly struck Iran at the end of February. Hezbollah had first re-ignited the cross-border conflict with projectiles fired at communities in Northern Israel in early March. While Lebanon and Israel agreed to a ceasefire Wednesday, Hezbollah rejected that agreement. Since then, continued Israeli airstrikes have killed nine people, including three members of the Lebanese military.

White phosphorus is not banned under international law, but it is illegal to use the chemical in and near populated areas since it can cause widespread harm. Israel has been accused by the international human rights community for decades of using the substance in a way that puts civilians in danger.

"It can create cruel injuries—life long injuries," says Ramzi Kaiss, a Lebanon researcher with the international NGO Human Rights Watch (HRW). "Or cause death."

White phosphorus is a solid, waxy chemical that ignites instantly when combined with oxygen. The Chemical Weapons Convention, an arms control treaty signed by more than 190 states, that focuses on the production and use of chemical weapons, designates white phosphorus an incendiary agent rather than a chemical weapon.

Countries can use the substance to create smoke screens, and the Israel Defense Forces say it's for this purpose that it uses the substance in some of its artillery shells. White phosphorus can also be used to mark military targets for subsequent strikes.