The UN agency for Palestinian refugees said today it would have to suspend food distribution in Gaza after Israel blocked humanitarian supplies from entering the strip.
Israel also prevented delivery of industrial diesel, which is paid for by the EU and used for the strip's sole power plant. Palestinian officials said the plant, which has already shut down once this week, would have to close by last night if no more fuel was delivered.
Israeli officials blamed Palestinian rocket fire out of Gaza. Peter Lerner, a spokesman for the Israeli defence ministry, said the border crossings were shut today because of "continued rocket fire and security threats at the crossings". For the past week Israel has also stopped journalists from entering Gaza.
It was not clear if food and fuel shipments would be allowed in tomorrow. Gaza's crossings close early Friday afternoon until Sunday morning.
The UN Relief and Works Agency (UNRWA), which supports Palestinian refugees and provides them with regular food baskets, said food distribution would have to stop from tomorrow. "Our warehouses are empty and our food distribution to 750,000 people will be suspended if we cannot get food in," said Christopher Gunness, an UNRWA spokesman.
The renewed fighting and delayed shipments signal the gradual collapse of a ceasefire in Gaza between Israel and Palestinian militant groups which had held for nearly five months. Last week Israel killed six Hamas gunmen in a raid into Gaza which they said was aimed at destroying a tunnel they feared would be used to capture Israeli soldiers.
Hamas, and other militant groups, began firing rockets into southern Israel and have continued over several days. Israeli troops then killed four Hamas gunmen in Gaza in an attack yesterday, and Palestinian militants responded by firing several rockets this morning into southern Israel.
"The UN has been very clear that we should not hand the agenda over to those who fire rockets," said John Ging, head of Gaza operations for UNRWA.
"They shouldn't dictate whether the crossings are open or not for the civilian population here."
Israel's deputy defence minister, Matan Vilnai, suggested the ceasefire might yet continue. "Without a doubt, it is faltering, but it isn't over," he told Israel Radio.
Earlier this week the Israeli prime minister, Ehud Olmert, travelled to an army base near Gaza and warned another military confrontation was coming.
"The question is not whether there will be a confrontation," he said, "but when it will take place, under what circumstances, and who will control these circumstances."