The Red Cross said Tuesday that it was investigating reports that an ambulance station was hit during what officials called the most terrifying night yet of violence in Gaza, which is suffering a full-blown humanitarian crisis.

The military offensive against Palestinian rocket squads launched by Israel Dec. 27 has left up to 600 dead and as many as 3,000 injured in Gaza so far, said Pierre Kraehenbuehl, head of operations for the International Committee of the Red Cross.

"The main message coming out of Gaza this morning is one of fear and frustration," Kraehenbuehl told reporters. "This past night was described to us over the phone this morning as being the most frightening of all to date."

With civilian casualties mounting and clean water supplies nearing breakdown, Kraehenbuehl said: "There is no doubt in my mind that we are dealing with a full-blown and major crisis in humanitarian terms."

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He said the Red Cross was looking into reports that a Palestinian Red Crescent ambulance station in the northern town of Jabaliya was hit during the night.

"This remains to be further confirmed, but it is a signal of the intensity of the conflict," said Kraehenbuehl.

"It was apparently necessary to use tractors to move debris out of the way to have access to the station," he said, but added that ICRC had no further information at this stage. "I cannot tell you if it was the result of collateral effect of bombing around the area."

Fragile power supplies, already weakened by Israel's 18-months embargo on the Hamas-controlled territory, also threaten to collapse, leaving up to half a million people without clean water and at risk of disease, he said.

Israel denies there is a humanitarian crisis in the densely populated strip.

Israel has given the Red Cross permission to bring medical supplies including blood and vaccines into the sealed-off territory, and a team of war surgeons was allowed in Monday to assist doctors treating the wounded at Gaza's main Shifa hospital.

But Kraehenbuehl said medical access is worsening as the campaign continues.