Palestinian militants in the Gaza Strip on Wednesday fired their first phosphorus shell into Israel, which exploded in an open area in the Eshkol area in the western Negev.
No injuries or damage were reported.
The phosphorus shell came as Gaza militants fired at least 16 rockets at southern Israel throughout the day Wednesday, causing no casualties.
White phosphorus is not considered a chemical weapon. Militaries are permitted under laws of warfare to use it in artillery shells, bombs and rockets to create smoke screens to hide troop movements as well as bright bursts in the air to illuminate battlefields at night.
However, the substance can cause serious burns if it touches the skin and can spark fires on the ground.
Human Rights Watch on Sunday accused Israel of firing artillery shells packed with white phosphorus over populated areas of Gaza during recent fighting, including a crowded refugee camp, putting civilians at risk.
Israel maintains that it uses munitions in complete accordance with international law.
Palestinian militants have fired at least 16 rockets into Israel since Wednesday morning, all of them hitting open areas near Ashdod, Ashkelon, Be'er Sheva and in the western Negev. Five Israelis in Ashdod were treated for shock.
No injuries or damage were reported in the attacks.
More than 15 rockets were fired at Israel Tuesday, some of them during a three-hour humanitarian truce. One rocket hit an Ashkelon educational institution, causing some damage.
The Shin Bet security service said Tuesday that Palestinian militants in Gaza have fired some 565 rockets and 200 mortar shells at southern Israel since the Israel Defense Forces launched its offensive on the Hamas-ruled coastal territory on December 27 - an average of more than 30 a day.
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