Palestinian nurses treat a man wounded in an Israeli air strike at a hospital in Gaza City, 31 Dec 2008

A senior United Nations official says many families in Gaza are facing a life-or-death situation as Israel continues its military offensive against Hamas.

U.N. humanitarian coordinator Maxwell Gaylord released a statement Wednesday calling on Israel to allow more humanitarian aid to flow into Gaza, which has been under a blockade.

Israel has said it will allow 2,000 tons more of food and medical supplies into Gaza, and will allow some wounded Gazans to seek medical treatment in Israel.

But Gaylord says it is crucial for the Karni border crossing to be opened to allow in wheat grain for the 750,000 people who rely upon U.N. relief.  He also says electricity needs to be fully restored to Gaza's hospitals, which are overwhelmed with patients.

Many other world powers and human rights groups have expressed concern about the humanitarian situation in Gaza.

The Palestine Red Crescent Society issued an emergency appeal for nearly $7 million on Wednesday to support its humanitarian efforts in Gaza. The aid organization is part of the International Red Cross.

Britain on Wednesday pledged $10 million in emergency aid for the Gaza Strip, calling the human cost of Israel's assault on the Palestinian territory "unacceptable."

Britain's aid minister, Douglas Alexander, expressed concern about dwindling medical supplies, food stocks and power cuts, which are affecting hospitals and other essential services in the Gaza Strip.

Greece's foreign ministry said it will send two planes with 30 tons of medical aid to Tel Aviv, which will then be transported to Gaza.

On Tuesday, Israel allowed about 100 aid trucks and five ambulances into Gaza.

Nearly 400 Palestinians have died in five days of Israeli air strikes, and hundreds more have been wounded.