The Israeli military has set up a committee headed by a colonel to investigate whether its soldiers fighting in the densely populated Gaza Strip improperly fired shells packed with white phosphorus, a powerful chemical munition that can cause serious or fatal burns, Israeli officials said Wednesday.

White phosphorus is legal under international law if it is used as a smokescreen to obscure troop movements, but an international convention bans targeting civilians with it.

Amnesty International issued a report Monday about shelling in a residential area of Gaza City, concluding that Israel used white phosphorus improperly. Doctors in Gaza reported treating patients with possible burns from the substance. Amnesty also said Israel used phosphorus shells in a Jan. 15 attack that set U.N. warehouses afire in Gaza City.