Israel and Hamas were urged to resume talks by the White House after Egyptian-mediated negotiations failed to extend a ceasefire and rocket fire resumed.
White House spokesman Josh Earnest told reporters: "The United States is very concerned about today's developments in Gaza."
He added: "We condemn the renewed rocket fire and we are concerned about the safety and security of civilians on both sides of that conflict."
There have been two days of quiet in Gaza. No rockets or missiles, no more destroyed houses, no more ambulance sirens screaming.
A three-year-old girl has been rescued from Gaza and brought to London for life-saving heart surgery.
A small team of NHS doctors and surgeons is travel to Gaza to set up facilities and establish how best to use specialists and equipment.