Medical staff and Hamas officials said at least 140 people were killed when missiles hit security compounds and militant bases across Gaza.
The strikes, the most intense Israeli attacks on Gaza in recent times, come after the expiry of a truce with Hamas.
Israel said it was responding to continued rocket attacks from Gaza.
Palestinian militants frequently fire rockets against Israeli towns from within the borders of Gaza.
In a statement, Israel's military said it targeted "Hamas terror operatives" as well as training camps and weaponry storage warehouses.
In the West Bank, Palestinian Authority President Mahmoud Abbas - whose Fatah faction was ousted from Gaza by Hamas in 2007 - condemned the attacks and called for restraint.
But Hamas quickly vowed to carry out revenge attacks on Israel in response to the air strikes, firing Qassam rockets into Israeli territory as an immediate reply.
"Hamas will continue the resistance until the last drop of blood," spokesman Fawzi Barhoum was reported as saying.
Israel also stood firm, saying operations "will continue, will be expanded, and will deepen if necessary".
Rising toll
Reports of the casualties in Gaza mounted swiftly after news broke of the Israeli operation.
Map
Palestinian militant group Hamas, which controls Gaza, initially said at least 40 people had been killed when a missile hit security headquarters in and around Gaza City.
That figure quickly rose until both Hamas and Palestinian doctors said at least 140 were killed and some 400 people injured.
Egypt opened its border crossing to the Gaza Strip at Rafah to absorb and treat some of those injured in the south of the territory.
Most of the dead and injured were said to be in Gaza City, where Hamas's main security compound was destroyed.
But casualties were also reported around Gaza, including in the southern town of Khan Younis, where Reuters news agency said at least 20 people were thought to have died.
Hamas said all of its security compounds in Gaza were destroyed by the Israeli air strikes, which Israel said hit some 40 targets across the territory.
The air strikes are the most intense Israel has launched against Gaza for some time, and come amid rumours that a ground operation is imminent.
Israeli security officials have been briefing about the possibility of a new offensive into Gaza for some days now, says the BBC's Paul Wood, in Jerusalem.
But most reports centred on the possibility of a ground offensive, and Prime Minister Ehud Olmert was not expected to authorise any operation until Sunday at the earliest.
http://news.bbc.co.uk/2/hi/middle_east/7800985.stm
This is more reason why the Middle East does not like the US. It is because we have Israels back too much.
Yep, US support Israel all the time, even when they are very wrong
Quote: from Anwar80 at 3:18 am on Jan. 2, 2009 Quote: from asia lover at 1:15 pm on Jan. 2, 2009 They both need to chill the fuck out. I know that they have been quarreling for a while now, but come on. You both have the same God. You both have souls, hearts, can feel love. The Israelis think they are better than the rest of the world. That they can get away with anything So attacking them will make things better? Personally I am with the Palestinians. Their land was taken from them, that was wrong. But now that the Israelis are there, learn to share. I am not saying it is going to be easy, but both parties attitudes have to change.
Quote: from asia lover at 1:15 pm on Jan. 2, 2009 They both need to chill the fuck out. I know that they have been quarreling for a while now, but come on. You both have the same God. You both have souls, hearts, can feel love. The Israelis think they are better than the rest of the world. That they can get away with anything
They both need to chill the fuck out. I know that they have been quarreling for a while now, but come on. You both have the same God. You both have souls, hearts, can feel love.
The Israelis think they are better than the rest of the world. That they can get away with anything
Agreed, but what happening now that Israel is keeping killing people in Gaza & no one is doing anything about it
Quote: from KathyN at 11:33 am on Dec. 27, 2008 Anwar80, do you want me to show pictures of Israelis towns after bombing? This almost made me laugh. - If you think you can justify the heinous - massacre type retaliation of Israelis, then reconsider. Killing innocent children and women and then asserting "we have been targetting Hamas"...Sheesh. Duping unfortunately isn't that easy. What Israeli army has been doing in Gaza is just ruthless and you should sympathise with the innocent Palestenians and acknowledge the factual scenario as a sane human being regardless of your personal political biases.
Anwar80, do you want me to show pictures of Israelis towns after bombing?
This almost made me laugh. - If you think you can justify the heinous - massacre type retaliation of Israelis, then reconsider. Killing innocent children and women and then asserting "we have been targetting Hamas"...Sheesh. Duping unfortunately isn't that easy. What Israeli army has been doing in Gaza is just ruthless and you should sympathise with the innocent Palestenians and acknowledge the factual scenario as a sane human being regardless of your personal political biases.
I want peace. I really do. But I don't think it is possible right now... :(
Quote: from KathyN at 2:33 pm on Dec. 27, 2008 Anwar80, do you want me to show pictures of Israelis towns after bombing? typical propaganda
Civilian deaths are unfortunate but at the same time Hamas and Palestinian's have been suicide bombing innocent Israeli's and are now firing away at Israel. I wouldn't expect them to just take it.
Because overall the situation is horrible, lets not act like the Israeli's are necessarily the bad guys.
Hopefully, both groups of people find peace eventually.