US Secretary of State Condoleezza Rice has blamed Hamas for breaking the ceasefire with Israel that led to renewed violence in Gaza.
"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," Rice said in a statement on Saturday.
"The ceasefire should be restored immediately," she added. "The United States calls on all concerned to address the urgent humanitarian needs of the innocent people of Gaza."
Earlier in the day, the US State Department had urged Israel to avoid civilian casualties after it launched attacks against the Islamic Hamas movement in the Gaza Strip.
"The US urges Israel to avoid civilian casualties as it targets Hamas in Gaza," US National Security Council spokesman Gordon Johndroe said in a statement.
"Hamas' continued rocket attacks into Israel must cease if the violence is to stop. Hamas must end its terrorist activities if it wishes to play a role in the future of the Palestinian people," Johndroe added.
The spokesman made the remarks hours after Israel attacked the Hamas-ruled enclave in retaliation for the continuing artillery firing by Hamas at southern Israel.
At least 225 people were killed in the Israeli air strikes. Israel's military said that it was ready to intensify its operations against the Palestinian militants in the Gaza Strip if needed.
Meanwhile, the White House said US President George W. Bush, who is at his ranch in Crawford, Texas, for Christmas vacation, has discussed the Middle East situation with Rice and received briefing on the Israeli air strikes from his national security adviser Stephen Hadley.
The president also talked over the phone to Saudi King Abdullah on "the Middle East", said Johndroe without providing further information.
US president-elect Barack Obama, who is in Hawaii for his holiday, is also "closely monitoring the Gaza situation", said his spokesperson on national security Brooke Anderson.