A Palestinian woman receives humanitarian aid at a UN food distribution center in Khan Younis refugee camp. (Reuters)

The UN aid agencies said the Karni and Nahal Oz crossings into Gaza from Israel "must remain open 24 hours a day if humanitarian need is to be adequately met."

UN Secretary General Kofi Annan on Saturday demanded immediate access for UN workers and humanitarian relief supplies to the Gaza Strip.

He said he was "extremely concerned about the dangerous situation in the occupied Palestinian Territory."

"The passage of foodstuffs and other essential supplies through the Karni commercial crossing should be ensured and restrictions on movement and access for UN agencies should be lifted forthwith," Annan said.

"I am appealing for urgent action to alleviate the desperate humanitarian situation of the civilian population."

The World Food Program (WFP) said it estimated in June 70 percent of Gaza's 1.4 million population already were unable to meet their daily food requirements without assistance.

It said wheat flour mills, food factories and bakeries were being forced to reduce production due to power shortages.

Israeli warplanes shelled the coastal Strip's only power plant on Wednesday, June 28, damaging the plant's six main electrical transformers, which provide up to 50 percent of the Strip with electricity.

Palestinian Central Bureau of Statistics (PCBS) said Friday, June 30, that About 200 thousand households lost the source of electricity, and 179 thousand households' refrigerators are not operating due to interruption of electricity current.

Supplies of sugar, dairy products and milk are running low due to limited commercial supplies from Israel, the WFP said.

As a result, food prices have increased by 10 percent in the past three weeks.

With less than a fourth of the fuel needed to pump backup generators, the water utility's daily operation has been cut by two thirds, resulting in water shortages and a "critical" situation at the sewage plants, said the United Nations Relief and Works Agency (UNRWA).

Since the June 28 bombing, the entire Gaza strip has been without electricity for between 12 and 18 hours each day.

The agency said generators that power Gaza's water wells and sewage pumping plants were running low of fuel.

The World Health Organization said the public health system was also facing an unprecedented crisis.

While Gaza's hospitals and 50 percent of its primary care clinics have generators, the stock of fuel to power them will last for a maximum of two weeks, according to WHO.

The agency said there has been a 160 percent increase in diarrhoea cases in the last week, compared with the same period last year.

WHO further estimated that 23 percent of the essential drug list will be out of stock within a month and expressed alarm about a tightening of restrictions on patients needing to leave Gaza for treatment.

The United Nations Human Rights Council decided on Thursday, July 6, to send a fact-finding mission to the occupied Palestinian territories to report on Israel's grave rights violations in the occupied lands.

Switzerland, the depositary state for the Geneva Conventions, has also accused Israel of breaking humanitarian law by inflicting "collective punishment" on Palestinians.

It stressed that there was "no doubt" that Israel had not taken the necessary precautions required of it under international law to protect the civilian population and infrastructure.