More than 200 Palestinians who fled their homes because of an Israeli offensive in southern Gaza sought shelter in a vacant U.N. school Saturday.

In a sign of the tensions, some of the displaced got into an argument over winning a spot at the shelter and gunfire erupted. Police said three officers were wounded in the melee.

"Living conditions are at a new low. It's a struggle to survive," said John Ging, the new head of the U.N. Relief and Works Agency (UNRWA) in Gaza.

Ging warned that Israel's military campaign, prompted by the kidnapping of an Israeli soldier two weeks ago, has lead to a humanitarian crisis. "Water, food, electricity, sanitation; these are the problems. The situation doesn't get more basic than that," he said.

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On Saturday, UNRWA oversaw the transfer of 235 people — or 36 families — who were moved from Shouka, a largely Bedouin area close to Gaza International Airport, to an elementary school in the southern town of Rafah.

Arriving with few possessions, the Bedouins crowded around a U.N. truck in the school's courtyard to receive mattresses. One group of men made tea in the courtyard, using a small gas canister.

"We fled our home near the airport because of tank fire and air fire. At one stage we were told by Israelis over a loudspeaker at night to leave our homes for our own safety," said Jihad Abu Zakkar, 45, the father of six children.

He said his children screamed through the night, and the family left home in the morning under a white flag.

Umm Issam, 50, said her family of seven left home every night in the past week to sleep under a tree, further away from the fighting. Issam said she decided to seek U.N. help when she realized her husband, who is ill, could no longer walk such distances each night.

The U.N. gave other Bedouin families who have livestock 18 tents to set up nearby so they could watch their cattle and sheep.

Israel launched its military offensive two weeks ago, after Hamas-allied militants kidnapped an Israeli soldier in a cross-border raid. Southern Gaza's long-closed airport was one of the first positions Israeli forces and tanks occupied. Gaza's borders with Israel and Egypt have been largely closed during the crisis.

The closure and the destruction of Gaza's only power station by the Israeli air force have led to a humanitarian crisis in the area, said Ging, the UNRWA chief.

He urged Israel to open supply routes at crossings such as Karni in southern Gaza, where he said 235 containers of U.N. food were waiting to cross.

He said the border closure also was preventing the United Nations from shipping its empty containers out of Gaza to be refilled and returned.

The Israeli military had no immediate comment.