GAZA - Israeli warplanes and combat helicopters pounded the Hamas-ruled Gaza Strip on Saturday, killing at least 155 people in the bloodiest day for Palestinians in more than 20 years of conflict.
Militants in the Gaza Strip responded with rocket salvoes that killed one Israeli man and wounded several others. Both sides said they were prepared to launch wider attacks.
Black smoke billowed over Gaza City, where the dead and wounded lay scattered on the ground after more than 30 air strikes destroyed Palestinian security compounds, including two where Hamas was hosting graduation ceremonies for new recruits.
The Israeli army said it had targeted "terrorist infrastructure" following days of rocket attacks from Gaza on southern Israel that caused some damage but few injuries.
The rocket attacks increased pressure on Israeli political leaders to act as a February 10 election approaches.
U.S. President George Bush's administration, in its last weeks in office, called on Hamas to halt cross-border rocket attacks and urged Israel to avoid civilian casualties but stopped short of calling for an end to the air strikes.
The Israeli army pledged more strikes if necessary, possibly targeting Hamas leaders.
Hamas said at least 100 members of its security forces were 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.
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.
The Islamist group, 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.
At the main police headquarters, some rescue workers beat their heads and shouted "God is greatest." One badly wounded man lying nearby quietly recited verses from the Koran.
HAMAS THREATENS TO UNLEASH "HELL"
Hamas threatened to unleash "hell" to avenge the dead, including possible suicide bombings inside Israel.
Palestinian President Mahmoud Abbas said the Israeli air campaign was "criminal" and called for the international community to intervene.
Palestinians staged protests rallies in East Jerusalem, Ramallah and Hebron, leading to scuffles with the Israeli army.
European Union Foreign Policy Chief Javier Solana called for an immediate ceasefire and urged "everybody to exert maximum restraint," his spokesman said.
Egypt also condemned the Israeli raids and said it would keep trying to restore a truce between Israel and Gaza. Arab foreign ministers were set to hold an emergency meeting in Cairo on Sunday or Monday to take a common position on the raids.
The White House appeared to put the onus on Hamas. "Hamas' continued rocket attacks into Israel must cease if the violence is to stop," spokesman Gordon Johndroe said.
At the main Gaza City graduation ceremony, uniformed bodies lay in a pile and the wounded writhed in pain. Rescuers carried those showing signs of life to cars and ambulances, while others tried to revive the unconscious.
Israel warplanes bombed 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, making them prime Israeli targets.
The air strikes followed a decision by Israeli Prime Minister Ehud Olmert's security cabinet to widen reprisals for cross-border Palestinian rocket attacks following the collapse of a six-month-old, Egyptian-brokered ceasefire a week ago.
Asked if an escalation of the assault could include targeted strikes against Hamas leaders, army spokeswoman Avital Leibovitch said: "Anything belonging to Hamas could be a target. You can interpret that as you like."
A five-day Israeli offensive in March killed more than 120 people, but Saturday's death toll would be the highest for Palestinians since their 1980s uprising.
Hamas armed wing spokesman Abu Ubaida said the Islamist group would "teach the enemy a lesson they will never forget." Hamas brushed aside Israeli threats to target its leaders.
In an interview on Al Arabiya television, an Arab broadcaster widely watched in Gaza, Olmert called on Hamas to stop firing rockets, saying he would not "hesitate to use Israel's might."
But Olmert and Israeli leaders have repeatedly said they did 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 an election just six weeks away.
Additional reporting by Dan Williams in Jerusalem, Peter Millership in London, Tabassum Zakaria in Washington; writing by Adam Entous; editing by Philippa Fletcher.