GENEVA (Reuters) - The UN food agency called on Israel on Friday to provide "permanent and unhindered access" for aid workers and relief goods to Gaza, where Palestinians face increasing shortages.

A World Food Program (WFP) spokesman said that despite some improvements after calls to Israel to let aid flow, the frequent closure of the key Karni crossing and Israel's military operations were hampering efforts to help civilians.

Israel, which launched a major offensive in the Gaza Strip last week to force militants to free an abducted soldier, has expanded the operation to halt cross-border rocket attacks.

"We are asking for permanent and unhindered access for humanitarian personnel and relief goods to Gaza whenever we need it. We think there needs to be a complete delinkage between the political environment and humanitarian needs," WFP spokesman Simon Pluess told a news briefing in Geneva.

The WFP said the Karni crossing was open for three days out of the last six, allowing it to bring sugar and oil into Gaza. It hoped to bring wheat flour in on Sunday.

The International Committee of the Red Cross (ICRC) said it had been able to get some food parcels, medical supplies and fuel into Gaza in the past week, but needs remained great.

Destruction of the only power plant had left the water supply and sanitation systems dependent on back-up generators that consume large amounts of precious fuel, it said.

"Access to drinking water may soon become a serious problem. There is still no acute shortage of food or medical supplies reported," Giorgios Georgantas, head of the ICRC office in Gaza, said in an interview posted on the agency's website on Friday.

"However, with the very restricted movement of goods coming into the Gaza Strip, there is an impending risk of shortages," he warned.

Goods need to flow regularly so as to satisfy the needs of the densely-populated strip's 1.4 million people, who rely heavily on imports of basic food items, Georgantas said.

The ICRC was receiving scores of phonecalls from Palestinian residents seeking its help either because of medical emergencies requiring evacuation or a lack of basic supplies, he added.

Pluess said food prices in Gaza rose 10 percent in June, due to the erratic opening of Karni for commercial goods.

"Many families can no longer afford meat, fish, dairy products or olive oil, and this is also related to a skyrocketing unemployment rate," he said.