GAZA (Reuters) - Israel launched air strikes on Gaza for a second successive day on Sunday, piling pressure on Hamas after 229 people were killed in one of the bloodiest 24 hours for Palestinians in 60 years of conflict with the Jewish state.
"Palestine has never seen an uglier massacre," said Hamas leader Ismail Haniyeh and his Islamist group, which has controlled the coastal territory since June 2007, vowed revenge including suicide bombings in Israel's "cafes and streets."
Israel bolstered armored and infantry forces along the Gaza Strip border, and a military spokesman said on Sunday: "The (Gaza) operation is continuous. It is still taking place."
The Jewish state said it was responding to "intolerable" almost daily rocket and mortar fire by Gaza militants that intensified after Hamas ended a six-month ceasefire a week ago.
The militant attacks caused some injuries, raising the stakes for Israeli leaders ahead of a February 10 election which surveys show the right-wing opposition Likud party may win.
Israel said its warplanes mounted about 100 strikes on Saturday and that Palestinian militants had fired some 70 rockets at the Jewish state, killing one Israeli man.
"There is a time for calm and a time for fighting, and now the time has come to fight," Defense Minister Ehud Barak said on television. He later ruled out any new truce with Hamas.
Black smoke billowed over Gaza City after Israel bombed more than 40 security compounds, and uniformed bodies lay in a pile and the wounded writhed in pain at a graduation ceremony for new recruits hosted by Hamas.
Some rescue workers beat their heads and shouted, "God is greatest." A wounded man quietly recited verses from the Koran.
More than 700 Palestinians were wounded in Saturday's attacks, said medical staff.
Israel said the operation was aimed at "terrorist infrastructure," and outgoing Prime Minister Ehud Olmert said it "may take time." Officials said Hamas leaders could be targeted.
In Damascus, top Hamas leader Khaled Meshaal called for a new Palestinian uprising against Israel. "We will not leave our land, we will not raise white flags and we will not kneel except before God," said Haniyeh.
Two Palestinians were killed when a mosque was bombed in Gaza City, Hamas and medical staff said. Israel said it targeted the mosque because it was used for "terrorist activities."
Israeli Foreign Minister Tzipi Livni, a leading candidate to become the next prime minister, called for international support against "an extremist Islamist organization ... that is being supported by Iran," Israel's arch-foe.
U.S. President George W. Bush's administration, in its final weeks in office, put the onus on Hamas to prevent more violence.
"The United States ... holds Hamas responsible for breaking the ceasefire and for the renewal of violence in Gaza," U.S. Secretary of State Condoleezza Rice said in a statement.
The United Nations and the European Union called for an immediate halt to all violence.
The U.N. Security Council met late on Saturday to discuss the situation in Gaza but it was not immediately clear whether the 15-nation body would take any formal action.
Palestinian President Mahmoud Abbas, whose Fatah forces were routed in Gaza when Hamas won control last year, said Israel's action was "criminal" and urged world powers to intervene.
Egypt said it would keep trying to restore the truce.
Saturday's death toll was the highest for a single day in the Israeli-Palestinian conflict since 1948, when the Jewish state was established.
Hamas estimated at least 100 members of its security forces had been killed, including police chief Tawfiq Jabber, along with at least 15 women and some children.
The group, which won a 2006 parliamentary election but was shunned by Western powers over its refusal to renounce violence and recognize Israel, said all its security compounds in the Gaza Strip were destroyed or seriously damaged.
Aid groups said they feared the Israeli operation could fuel a humanitarian crisis in the impoverished coastal enclave, home to 1.5 million Palestinians, half of them dependent on food aid.
Gaza hospitals said they were running out of medical supplies because of an Israeli-led blockade.
(Additional reporting by Dan Williams, Allyn Fisher-Ilan, Douglas Hamilton and Jeffrey Heller in Jerusalem, Ari Rabinovitch in Tel Aviv and Wafa Amr in Ramallah, Peter Millership in London, Tabassum Zakaria in Washington; Editing by Ralph Gowling)