According to the Times newspaper, there is also evidence that the firing of rounds of WP, which is prohibited under international law, has injured Palestinian civilians, causing severe burns.
The daily said Thursday it had identified stockpiles of WP shells from high-resolution images taken of Israel Defense Forces (IDF) artillery units on the Gaza border this week.
The pale blue 155mm rounds are clearly marked with the designation M825A1, an American-made WP munitions. The shells were said to be an improved version with a more limited dispersion of the phosphorus, which ignites on contact with oxygen.
The rounds, which are being used to create a smokescreen on the ground, explode into a shower of burning white streaks and, were first identified by The Times at the weekend when they were fired over Gaza at the start of Israel's ground offensive.
"Artillery experts said that the Israeli troops would be in trouble if they were banned from using WP because it is the simplest way of creating smoke to protect them from enemy fire," the newspaper said.
Mads Gilbert, a Norwegian war surgery specialist working in Gaza, said that he had seen injuries believed to have resulted from Israel's use of a new "dense inert metal explosive" that caused "extreme explosions".
Although the shells are not defined as an incendiary weapon by the Third Protocol to the Convention on Conventional Weapons, Neil Gibson, technical adviser to Jane's Missiles and Rockets, insisted that the M825A1 was a WP round.
"The M825A1 is an improved model. The WP does not fill the shell but is impregnated into 116 felt wedges which, once dispersed [by a high-explosive charge], start to burn within four to five seconds," Gibson said.