All were employees for World Central Kitchen, a charity which provides food for displaced Palestinians.
Ismail al Thawabta, a spokesperson for the Gaza government’s media office, said Israel was responsible for their deaths.
The Israeli military said it is “conducting a thorough review at the highest levels to understand the circumstances of this tragic incident”.
“The IDF makes extensive efforts to enable the safe delivery of humanitarian aid,” it said in a statement, adding that it has been working closely with the World Central Kitchen “in their vital efforts to provide food and humanitarian aid to the people of Gaza”.
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Aid airdropped over Gaza
Footage showed the bodies of the individuals at al Aqsa Martyrs hospital in the central Gaza town of Deir al Balah. Several of them wore protective clothing marked with the charity’s logo.
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The workers’ car was hit by an airstrike just after crossing from northern Gaza.
It is believed they were helping to deliver aid that had arrived hours earlier on a ship from Cyprus, Mahmoud Thabet, a paramedic from the Palestinian Red Crescent who was on the team that brought the bodies to the hospital, told The Associated Press.
The World Central Kitchen called the incident a “tragedy”.
In a statement, it said: “We are aware of reports that members of the World Central Kitchen team have been killed in an IDF attack while working to support our humanitarian food delivery efforts in Gaza. This is a tragedy.
“Humanitarian aid workers and civilians should never be a target. Ever.”
It said it would share more information when it has “gathered all the facts”.
In an earlier statement, Mr al Thawabta called for a stop to the war.
He added: “It is time for the killing against civilians, against children, and against women to stop.”
Mr al Thawabta went on to urge “all countries of the world, all international organisations, and all human rights organisations to condemn this crime immediately”.
The aid ships that arrived on Monday carried some 400 tons of food and supplies in a shipment organised by the United Arab Emirates and the World Central Kitchen.
The charity was founded by celebrity chef Jose Andres in 2010, who first sent food to Haiti after an earthquake.
The organisation said last month it had served more than 42 million meals in Gaza over 175 days.