Nonetheless, Gaza Strip residents and Reuters witnesses said Israeli shelling and Hamas missile launches had slowly quietened down through the afternoon, suggesting a de-facto truce might be taking shape as an international efforts to broker a permanent ceasefire appeared to flounder.
U.S. President Barack Obama, speaking by phone on Sunday with Israeli Prime Minister Benjamin Netanyahu, stressed the need for an immediate, unconditional humanitarian ceasefire in Gaza, the White House said.
Urging a permanent end to hostilities on the basis of the 2012 ceasefire agreement, Obama added that "ultimately, any lasting solution to the Israeli-Palestinian conflict must ensure the disarmament of terrorist groups and the demilitarization of Gaza.''
Read MoreMore fighting in Gaza after rockets hit Israel
Israel's military has said it will need more time to destroy a warren of tunnels that criss-cross the Gaza border that it says is one of its main objectives.
Israel and the Hamas Islamists who control Gaza had agreed to a 12-hour ceasefire on Saturday to allow Palestinians to stock up on supplies and retrieve bodies from under the rubble.
Netanyahu's cabinet voted to extend the truce until midnight on Sunday at the request of the United Nations, but called it off when Hamas launched rockets into Israel during the morning.
Palestinian medics said at least 10 people had died in the wave of subsequent strikes that swept Gaza, including a Christian woman, Jalila Faraj Ayyad, whose house in Gaza City was struck by an Israeli bomb.
Some 1,031 Palestinians, mainly civilians and including many children, have been killed in the 20-day conflict. A Gaza health ministry official issued revised figures of dead, saying that 30 fewer people than thought had died in the conflict.
Israel says 43 of its soldiers have died, along with three civilians killed by rocket and mortar fire out of the Mediterranean enclave.