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GAZA CITY, Gaza Strip -- Israeli forces fired a tank shell at a hospital in Gaza on Monday, killing at least four people and injuring 40 others, health officials said.

It was the third hospital Israel's military has struck since launching a ground offensive in Gaza last week.

The four people killed at al-Aqsa Hospital on Monday included one patient and three visitors, health officials told NBC News.

Health Ministry spokesman Ashraf Al-Qidra told Reuters that the tank shell hit the third floor of the building that houses an intensive care unit and operating rooms.

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The Hamas-run al-Aqsa TV station showed chaotic footage from the scene, including what it said was an ambulance driver being wheeled inside on a stretcher and a doctor with a neck wound.

Speaking to the station, deputy hospital manager Dr. Faiz Zaidan said: "I urge the Red Cross and its hospitals to come and transfer as many cases as possible, we have nothing to offer to patients." He added that shrapnel had been found in the facility's reception area.

Another doctor, who was not identified, added: "The Israeli aggression, they could not find any targets to hit, so they started hitting hospital, hitting patients."

15 minutes of non-stop artillery shelling coming from East #Gaza. The barrage of shelling has been unrelenting today #hamas #israel -Ayman Mohyeldin (@AymanM) July 21, 2014

Israel has defended shelling civilian-inhabited areas where Hamas allegedly hides rockets.

The strike came just hours after charity Medecins Sans Frontieres said health workers in Gaza were coming under fire and urged Israel to stop its strikes.

Gaza's Wafa hospital was evacuated and then "obliterated" by more than 15 direct hits from Israeli forces on Friday, senior nurse Ali Hassan said in an interview with the U.K.'s Channel 4 News.

More than 500 Palestinians, most of whom were civilians, and 20 Israeli soldiers have died during two weeks of bombing as well as a ground invasion launched into Gaza on Thursday.

Reuters contributed to this report.