Hamas
Peter Lerner accused the BBC of "accepting at face value" what Hamas says.
The Hamas-run Gaza Health Ministry says a massive blast hit a Gaza City hospital packed with wounded and other Palestinians seeking shelter, killing hundreds of people.
Joe Biden is already on his way to the crisis-torn region.
There are growing worries about the humanitarian needs of people in Gaza and Israel.
"Did you have any indication of what was going to happen ten days ago?"
The broadcaster has already come under fire for its coverage of the Israel-Hamas war.
Maoz Inon is a prominent peace activist who does not want "revenge" for his parents' death.
The Palestinian territory is currently under siege.
"No one should pretend this is going to be anything but horrific."
"I feel that the worst is yet to come," emergency relief coordinator Martin Griffiths said as the humanitarian crisis worsens for Palestinians in Gaza.