The White House issued a statement blaming Hamas for the Israeli air strikes on Gaza that killed hundreds of Palestinians in the bloodiest day there in decades.
Hamas must end "terrorist activities" if it wished to play a role in the future of the Palestinian people, the statement said.
"The United States strongly condemns the repeated rocket and mortar attacks against Israel and holds Hamas responsible for breaking the ceasefire and for the renewal of violence in Gaza. The ceasefire should be restored immediately," said the statement, attributed to Secretary of State Condoleezza Rice.
"The United States calls on all concerned to address the urgent humanitarian needs of the innocent people of Gaza."
"Hamas' continued rocket attacks into Israel must cease if the violence is to stop,” Gordon Johndroe, a spokesman for the National Security Agency, said in a statement.
Click here for photos (WARNING: Graphic).
The president was briefed on the situation in Israel and Gaza and spoke by phone to Rice earlier in the day. A statement from Crawford, Texas, was scheduled for late Saturday.
Meanwhile, President-elect Obama was receiving daily briefings on the Middle East at his residence in Hawaii, officials said.
"[He] is closely monitoring global events, including the situation in Gaza, but there is one president at a time," said chief NSA spokesman Brooke Anderson.
A series of simultaneous strikes caused widespread panic and confusion Saturday as black smoke rose above Gaza. At least 200 people were killed and more than 400 wounded. Officials said others were still buried under the rubble, the Associated Press reported.
The strike came in response to a barrage of rocket and mortar fire from Hamas-controlled Gaza to southern Israeli towns through the week. Israel warned Hamas Friday that it was verging on an invasion of the Gaza strip.
Reuters reported a rocket fired by militants Saturday killed one person in southern Israel. Another two in the Israeli town of Netivot were wounded.
The European Union urged an immediate halt to Israeli air strikes and Palestinian attacks in and around Gaza, the AP reported.
The current EU president in France said the bloc "condemns the disproportionate use of force" from both sides.
The statement urges the "reopening of all checkpoints and the immediate resumption of fuel and humanitarian aid deliveries."
The statement Saturday says "there is no military solution in Gaza" and urges a lasting truce.
French President Nicolas Sarkozy, in a separate statement, expressed "great concern" about the escalating violence by Israelis and Palestinians.
Israeli Defense Minister Ehud Barak says Israel's air offensive against militant sites in Gaza "will widen as necessary."
Barak says Israel does not intend to allow Islamic Hamas militants who rule Gaza to continue firing rockets and mortars on Israel's southern communities.
Barak says there is a time for calm and a time for fighting. Speaking at a news conference Saturday, he said "now is the time for fighting" and that "the operation will expand as necessary."
"Anything belonging to Hamas could be a target. You can interpret that as you like," Reuters quoted an Israeli military spokeswoman as saying. The Israeli Defense Forces said the operations will “be continued, expanded and intensified as much as required."