Bush says Hamas to blame for Gaza
The UN has warned of a growing humanitarian crisis
President Bush has blamed the violence in Gaza and southern Israel firmly on Hamas, after a week of Israeli air strikes and Palestinian rocket attacks.
Mr Bush, who has just weeks left in office, said Hamas was a terrorist group dedicated to destroying Israel.
Earlier the Hamas leader-in-exile, Khaled Meshaal, warned Israel of a "black destiny" if it began a threatened ground offensive on Gaza.
Hamas said one of its military leaders died in an overnight strike.
I urge all parties to pressure Hamas to turn away from terror and to support legitimate Palestinian leaders working for peace
Abu Zakaria al-Jamal died of his wounds after a raid.
Israel has now carried out more than 700 strikes on Gaza since launching the offensive a week ago, AFP news agency said.
The UN warned of a worsening humanitarian crisis in Gaza.
The UN said it believed 25% of more than 400 Palestinians killed by Israeli action so far were civilians.
In his weekly radio address President George W Bush said Hamas was responsible for the latest violence and rejected any unilateral ceasefire that he said would allow Hamas to continue to fire on Israel.
He added that no peace deal would be acceptable without tougher action to prevent Hamas and other groups from receiving weapons.
"There must be monitoring mechanisms in place to help ensure the smuggling of weapons to terrorist groups in Gaza comes to an end," he said.
"I urge all parties to pressure Hamas to turn away from terror and to support legitimate Palestinian leaders working for peace," Mr Bush added.
Israeli air strikes on Gaza continued early on Saturday, with 35 reported. One person was killed as large parts of the American school in north-west Gaza were destroyed.
Israel has threatened to launch a ground offensive. It has called up army reservists, and tanks and troops are massed on the Gaza frontier.
BBC Middle East Editor Jeremy Bowen says a week of bombardment has not been able stop militant rocket attacks, and Israel now has to decide whether to send in ground troops.
But in a pre-recorded statement broadcast on al-Jazeera TV, Damascus-based Khaled Meshaal said Israel would be making a "foolish mistake" if it sent tanks into Gaza.
Speaking publicly for the first time since Israeli air strikes started a week ago, he said Hamas resistance and infrastructure were intact.
"We will not break, we will not surrender or give in to your conditions," Mr Meshaal said in a speech aimed at the Israelis, the Palestinians and the wider Muslim world.
To them, Mr Meshaal said this was not a battle against Hamas alone, but against the entire umma, or nation.
Analysts say this was an apparent reference to a populist Islamist idea that the Palestinians are defending the Muslim world against a modern form of Crusades.
The UN said the Israeli military escalated its offensive against the Hamas leadership in Gaza on Friday, targeting the homes of more than 20 Hamas officials in its latest air strikes.
In response, Palestinian militants fired on Israel, their missiles injuring four people in the southern city of Ashkelon. More than 20 more missiles were fired on Saturday morning.
Four Israelis have been killed so far by militant rocket fire.
Israel is refusing to let international journalists into Gaza, despite a Supreme Court ruling to allow a limited number of reporters to enter the territory.
The UN says the week-long assault has worsened the crisis in Gaza, despite an increase in humanitarian shipments.
Israel tightened its control of what gets in and out of the crowded coastal Strip after Hamas, the elected power, seized control of the area from rival Fatah forces 18 months ago.
Since then, the UN says there has been a significant deterioration in infrastructure and basic services, with 80% of the 1.4m population unable to support themselves.