"The suffering caused to civilian populations as a result of the large-scale violence and destruction that have taken place over the past few days has saddened me profoundly," he said.
'Bitter end'
Forty people were said to have been wounded in Tuesday's raids, which targeted Hamas-run offices and security installations, Palestinian officials said.
UN Secretary General Ban Ki-moon has called for an immediate ceasefire
Meanwhile, an Israeli naval vessel has blocked pro-Palestinian activists trying to carry medical aid to Gaza by sea and escorted their boat back to Cyprus.
The two vessels collided during the incident, causing damage to both boats but no injuries. The activists said the naval vessel had rammed them after they ignored warning shots fired across their bow.
Israel's defence chief earlier said his country was fighting a "war to the bitter end" against Hamas.
The UN says at least 62 of the Palestinians killed so far have been women and children.
Israel has massed forces along the boundary with Gaza and has declared the area around it a "closed military zone".
Correspondents say the move - in addition to the call-up of thousands of reservists - could be a prelude to ground operations, but could also be intended to build pressure on Hamas.
The Red Cross earlier described the situation in Gaza's hospitals as chaotic, with medical teams "stretched to the limit".
Trucks laden with medical aid have been permitted to cross into Gaza from Egypt at the Rafah crossing.
European Union foreign ministers are scheduled to meet in Paris later (1730 GMT) to discuss the escalating crisis.
The meeting, hosted by French Foreign Minister Bernard Kouchner, is expected to consider the idea of an humanitarian aid corridor, and how to bring additional aid to Gaza.
Angry protests
Dozens of Hamas centres, including security compounds, government offices and tunnels into Egypt, have been hit since Israel started its massive bombing campaign on Saturday morning.
Israel says its aim is to end the rocket attacks by Hamas-linked militants - of which there were reportedly more than 40 on Monday.
Defence Minister Ehud Barak said Israel wanted to deal Hamas a "severe blow" and its operation would be "widened and deepened as needed".
The US - Israel's strongest ally - said the onus was on Hamas to end the violence and commit itself to a truce, but there have been angry protests against the offensive in many cities across the Arab world and in several European capitals.
The strikes began less than a week after the expiry of a six-month-long ceasefire deal with Hamas, which has controlled Gaza since 2007.
Israel withdrew in 2005 but has kept tight control over access in and out of Gaza and its airspace.
GAZA VIOLENCE 27-29 DECEMBER
1. Ashdod: First attack so far north, Sunday 2. Ashkelon: One man killed, several injured in rocket attack, Monday 3. Sderot: rocket attacks 4. Nevitot: One man killed, several injured in rocket attack, Saturday 5. Civilian family reported killed in attack on Yabna refugee camp, Sunday 6. Israeli warplanes strike tunnels under Gaza/Egypt border, Sunday 7. Three young brothers reported killed in attack on Rafah, Sunday 8. Khan Younis: Four members of Islamic Jihad and a child reported killed, Sunday 9. Deir al-Balah: Palestinians injured, houses and buildings destroyed, Sunday 10. Interior ministry and Islamic University badly damaged, Monday 11. Gaza City port: naval vessels targeted, Sunday 12. Shati refugee camp: Home of Hamas leader Ismail Hanniyeh targeted, Monday 13. Intelligence building attacked, Sunday 14. Jebaliya refugee camp: several people killed in attack on mosque, Sunday
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