The UN suspended food distribution to 750,000 people in Gaza yesterday and much of its main city was without power last night after Israel halted supplies to the Strip amid continued fears that the five-month-old ceasefire could break down.

Earlier, the Israeli authorities turned away 20 senior European diplomats from the Erez crossing as they attempted to visit Gaza. The diplomats – including Richard Makepeace, the British Consul-General – were given no reason by staff at the crossing, a Consulate spokeswoman said.

The move followed more than a week in which foreign journalists have also been barred from entering Gaza. The Foreign Press Association has protested against the ban, which observers say has lasted for longer than any other of its kind since the intifada began eight years ago.

Crossings have been mainly closed between Israel and Gaza since the Israeli military killed six Hamas militants in a raid into Gaza nine days ago which it said had thwarted a kidnap attempt. The raid was followed by rocket fire from inside Gaza and further raids against militants. Israel had originally said it would allow 30 trucks to deliver supplies into Gaza yesterday.

But Peter Lerner, a spokesman for military co-ordination between Israel and the occupied territories, said: "Our plans to facilitate the needs of international organisations were thwarted by Palestinian activity. We were not willing to risk the lives of those opening the crossings."

However, John Ging, the Director of Operations for the UN refugee agency UNRWA which said it had had to suspend the food distribution said: "The UN has been very clear that we should not hand the agenda over to those who fire rockets. They shouldn't dictate whether the crossings are open or not for the civilian population here."

Gaza energy officials shut down the Strip's own power plant, after Israel cancelled plans to ship in some diesel fuel for the plant. The Israeli move came after Gaza militants fired at least eight rockets and some mortar shells at Israel on Thursday, according to the Israeli military. A total of 11 militants have been killed since sporadic fighting resumed last week.

Israeli officials said that the diplomats were not admitted to Gaza because their mission was not a humanitarian one. The Israeli authorities have insisted that that Erez is only open for humanitarian cases.