GAZA (Reuters) -- Israeli warplanes and helicopters pounded the Hamas-ruled Gaza Strip, killing at least 225 people in the bloodiest one-day death toll in 60 years of conflict with the Palestinians.
Militants in the Gaza Strip, who have launched dozens of rocket attacks against Israel since a truce expired just over a week ago, fired more salvoes that killed one Israeli man and wounded several others.
Both sides said they were ready to stage wider assaults, threatening to plunge the region into a crisis that could leave stalled talks over Palestinian statehood in tatters.
Black smoke billowed over Gaza City, where the dead and wounded lay scattered on the ground after Israel bombed more than 40 security compounds, including two where Hamas was hosting graduation ceremonies for new recruits.
At the main Gaza City graduation ceremony, uniformed bodies lay in a pile and the wounded writhed in pain. Some rescue workers beat their heads and shouted "God is greatest." One badly wounded man quietly recited verses from the Koran. 'Solid Lead'
More than 700 Palestinians were wounded in all, medics said. Israel said the operation, dubbed "Solid Lead," targeted "terrorist infrastructure" following days of rocket attacks on southern Israel that caused damage but few injuries. An army spokeswoman said Hamas leaders could be targeted.
There is a time for calm and a time for fighting, and now the time has come to fight.
"There is a time for calm and a time for fighting, and now the time has come to fight," Defense Minister Ehud Barak said.
The rocket attacks increased pressure on Israeli political leaders to act as a February 10 election approaches.
The army did not set a timeframe but the mayor of Ashkelon, an Israeli city in range of Hamas's rockets, said military planners saw the operation lasting "more than a week."
Foreign Minister Tzipi Livni, a leading candidate to become Israel's next prime minister, called for international support against "an extremist Islamist organisation ... that is being supported by Iran," Israel's arch-foe.
In line with the Jewish state, the administration of U.S. President George W. Bush, in its final weeks in office, appeared to put the onus on Hamas to prevent a further escalation.
"Hamas' continued rocket attacks into Israel must cease if the violence is to stop," White House spokesman Gordon Johndroe
said in a statement that urged Israel to avoid civilian casualties but stopped short of calling for an end to the Israeli air strikes.
The United Nations and the European Union, in contrast, called for an immediate halt to all violence. Air Campaign 'Criminal'
Palestinian President Mahmud Abbas said the Israeli air campaign was "criminal" and urged world powers to intervene.
Egypt said it would keep trying to restore the truce between Israel and Gaza.
Hamas threatened to unleash "hell" to avenge the dead, including possible suicide bombings inside Israel. Hamas estimated that at least 100 members of its security forces had been killed, including Police Chief Tawfiq Jabber and the head of Hamas's security and protection unit, along with at least 15 women and some children.
Morgues across the Gaza Strip ran out of space for bodies.
The Islamist group, which won a 2006 parliamentary election but was shunned by Western powers over its refusal to renounce violence and recognize Israel, said all of 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 the Israeli-led blockade, increasing the chances that the death toll will rise.
Palestinians staged protest rallies in Arab East Jerusalem, and in the West Bank cities of Ramallah and Hebron, leading to scuffles with Israeli forces.
Israeli analyst Ron Ben-Yishai said the strike was "shock treatment ... aimed at securing a long-term cease-fire between Hamas and Israel on terms that are favorable to Israel." Widen Reprisals
Among the buildings destroyed in the Israeli bombardment was Gaza's presidential compound, which Hamas seized in June 2007 from Abbas's secular Fatah forces after a brief civil war.
Witnesses also reported heavy Israeli bombing along Gaza's border with Egypt. Palestinians use hundreds of tunnels under the border to bring in everything from goods to weapons.
The campaign followed a decision by Israeli Prime Minister Ehud Olmert's security cabinet to widen reprisals for crossborder Palestinian rocket attacks following the collapse of a six-month-old, Egyptian-brokered cease-fire a week ago.
A five-day Israeli offensive in March killed more than 120 people, but the December 27 death toll was the highest for a single day since 1948, when the Jewish state was established.
Olmert, who will leave office after the February election, has repeatedly said Israel does not want to retake control of the Gaza Strip. Israel pulled its ground forces and settlers out of the coastal territory in 2005.
After a 2006 war in Lebanon that many Israelis viewed as a failure, military action in Gaza has become a political hot potato that could affect the outcome of the election.