FACTBOX - Key facts about white-phosphorus weapons

(Reuters) - Human Rights Watch accused Israel on Saturday of using white-phosphorus munitions during its offensive in the Gaza Strip.

The Israeli army said it would not provide details about the munitions it was using in the Gaza Strip, but it added: "We emphasise that the IDF (Israeli army) only employs weapons permitted by international law."

The army confirmed in 2006 that it had used phosphorus shells during its war against Hezbollah guerrillas in Lebanon.

Following are key facts about white phosphorus:

MILITARY APPLICATIONS

White phosphorus munitions are primarily used to make smoke screens or mark targets as a signalling mechanism, but also as an incendiary weapon. Human Rights Watch said Israel appeared to be using the munitions to hide its military operations -- "a permissible use in principle under international humanitarian law." White phosphorus is not considered a chemical weapon under international conventions. It is a colourless or yellowish translucent wax-like substance that smells a bit like garlic. The substance ignites easily in air at temperatures of about 30 degrees Celsius (86 Fahrenheit), and its fire can be difficult to extinguish.

INTERNATIONAL ACCORD

The Convention on the Prohibition of Use of Certain Conventional Weapons went into effect in 1983. Protocol III of the convention prohibits the use of incendiary weapons against civilians. The protocol also forbids their use against military targets within concentrations of civilians, except when the targets are clearly separated from civilians and "all feasible precautions" are taken to avoid civilian casualties.

USED BY U.S. MILITARY IN IRAQ