Israeli jets have attacked the Gaza Strip for a fourth day, with raids on a number of Hamas government buildings and security installations, report agencies.
Air strikes early Tuesday killed at least 10 people, medical officials in the coastal enclave said.
UN Secretary General Ban Ki-moon has called for an immediate ceasefire and condemned both Israel and Hamas.
About 320 Palestinians have died since Saturday, the UN says. Four Israelis have been killed by rockets from Gaza. One was a soldier, the first member of the military to die since the current fighting began.
While recognising Israel's right to defend itself from militant rocket attacks, Mr Ban condemned its "excessive use of force".
"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.
Forty people were said to have been wounded in Tuesday's raids, which targeted Hamas-run offices and security installations, Palestinian officials said.
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.
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.
Palestinian children search the ruins of a destroyed house following an Israeli air strike in the northern Gaza Strip, 29 December 2008
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.
Meanwhile: Israel rejected any truce with Hamas Islamists on Tuesday and said it was ready for "long weeks of action" on a fourth day of the fiercest air offensive in the Gaza Strip in decades.
As Israeli armored vehicles and troops were massed along the border for a possible invasion, Israeli warplanes pressed on with strikes, killing 12 Palestinians, including a pair of sisters, aged 10 and 12, in attacks on Hamas targets.
Medical officials put the total Palestinian death toll since Israel launched its offensive on Saturday as Gaza gunmen stepped up rocket fire, at 348 and more than 800 wounded. A United Nations agency said at least 62 of the dead were civilians.
The latest Israeli attacks came hours after rockets fired by Gazan militants killed an Israeli soldier near the border with Gaza and a civilian in the city of Ashdod.
With six weeks to go to an election that polls suggest the hawkish right-wing Likud party will win, Israel's centrist government says the offensive aims to put a stop to the rockets.
Israeli Interior Minister Meir Sheetrit said "there is no room for a ceasefire" with Hamas before the threat of rocket fire has been removed. "The Israeli army must not stop the operation before breaking the will of the Palestinians, of Hamas, to continue to fire at Israel," he told Israel Radio.
The Israeli military "has made preparations for long weeks of action," added Matan Vilnai, a deputy defense minister, in separate broadcast remarks.
Hamas spokesman Fawzi Barhoum has urged Palestinian groups to respond using "all available means" against Israel, including "martyrdom operations," meaning suicide bombings.
Israeli missiles flattened five ministerial buildings and a structure belonging to the Islamic University in Gaza City on Tuesday, witnesses said.
Another strike in northern Gaza's Beit Hanoun, killed two young girls taking out the trash near their home, medical workers and witnesses said. Later a security man was killed in a strike on a headquarters in Khan Yunis, medics and Hamas said.
Israel pounds Gaza for fourth day, 10 dead
FE Team | Published: December 31, 2008 00:00:00 | Updated: February 01, 2018 00:00:00
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