United States President George Bush has again emphasised what he calls Israel's right to protect itself, saying the crisis in Gaza is the fault of Hamas.
But President-elect Barack Obama, who takes office in two weeks, has so far refused to comment on the crisis, saying the US can have only one president at a time.
Mr Obama says he is being briefed on the situation every day.
Meanwhile, diplomatic efforts to end the fighting are gathering momentum.
France has drafted a United Nations Security Council resolution demanding a ceasefire in Gaza, but Israel vowed to continue military action until Hamas stops firing rockets.
Discussions between French, Arab and other Western delegations at the UN intensified on Monday.
Diplomats said the French resolution would include the deployment of international monitors to police any ceasefire agreement.
Palestinian Foreign Minister Riyad al-Malki told reports that Arab nations want a resolution demanding an immediate end to "Israeli aggression" in Gaza.
Arab League chief Amr Moussa also said Arab nations do not want to explicitly condemn Hamas.
However, Israeli ambassador Gabriela Shalev said there was no point in the Security Council passing any ceasefire resolution while Hamas continued to fire rockets at Israel.
She also rejected the idea of a resolution treating Israel and Hamas as equal parties. Hamas does not recognize Israel's right to exist.
The attacks began on 27 December after Hamas ended a six-month ceasefire on 19 December.
British ambassador John Sawers said there would be "a lot of intensive diplomacy over the next 48 hours".