The international Red Cross issued a dire warning on the state of basic services in Gaza on Tuesday, calling on Israel to lift a blockade it has imposed in response to increased rocket attacks by Palestinian militants.

Israel eased the siege for a day on Tueday, allowing in shipments of fuel and medicine. But the International Committee of the Red Cross said aid needed to be allowed into the territory on a regular basis to prevent a complete collapse of health and sanitary services.

"Deliveries of essential humanitarian goods must be secured in the long run to prevent more hardship and to avoid the collapse of the already fragile infrastructure," said Dorothea Krimitsas, a spokeswoman for the International Committee of the Red Cross.

Israel sealed Gaza on Thursday, halting fuel shipments. Three days later, Gaza's Hamas rulers shut down the territory's only power plant, which provides electricity to about one-third of Gaza's 1.5 million residents.

Krimitsas said the situation remained precarious. Gaza's hospitals were pooling their fuel to maintain life-saving services such as surgery and intensive care units.

Medical supplies are running out and health staff are having problems getting to work because transportation has become more difficult, Krimitsas told reporters.

"There is no functioning central heating in the hospitals," she added.

The ICRC, which acts as the guardian of the Geneva Conventions on the rules of warfare, has repeatedly called on both Israeli armed forces and Palestinian militants to ensure that their conflict avoids harming civilians.

Krimitsas said Israel needed to provide conditions for Palestinians to live normal lives without relying forever on emergency relief.

"Humanitarian aid alone cannot help contain the crisis," she said. "What is needed are political steps ... to ensure that enough imports are allowed into Gaza to make life bearable."