Palestinian villagers said the shelling came from the direction of the Israeli border, less than a mile away, scattering flaming objects in their midst and burning down 20 homes and the local United Nations-run school.

"One landed in my kitchen and caused a fire," said Zohair Mohammed abu Rejila, 35. "I went to put it out, but another one landed on Mayar, my baby daughter. It was like a block of fire, a piece of plastic on fire. When I knocked it off her, it exploded and out came this heavy white smoke with a very bad smell."

Doctors who treated Abu Rejila, his family and dozens of neighbors in southern Gaza said they were apparent victims of white phosphorus fired from Israeli artillery. One woman was killed.

They were the first suspected casualties of the munitions, which armies use as smoke screens for their movements or as incendiary devices, during Israel's 16-day-old assault on Hamas militants in the Gaza Strip.

Yousef abu Rish, director of the Nasser Hospital in Khan Yunis, said 55 people from nearby Khoza were treated for burns, breathing difficulties, and throat and eye irritation after exposure to toxic white smoke from shells fired just after midnight Sunday.

Abu Rish said he believed the smoke was white phosphorus gas, which is released when artillery bursts send scores of phosphorus wafers into the air that burst into flames.

"We need experts to test these shells," he said, "but we see the dangerous results."

Capt. Guy Spigelman, an Israeli spokesman, said the army was not aware of any military activity in the area at the time. He would not comment on whether the army was using white phosphorus.

Marc Garlasco, a senior military analyst for Human Rights Watch, said that in recent days he had observed Israeli artillery firing multiple airbursts of white phosphorus over the border toward the Gaza City area.

Abu Rejila said he and his family escaped before flames destroyed their apartment. His wife and daughter were being treated at Nasser Hospital.

Hanan Annajar, 41, was killed during the attack. Her son said a projectile hit her father's home, which burst into flames.