Gaza City hit by fresh Israeli air strikes after lull
Israel has carried out more air strikes on the Gaza Strip, having put 75,000 army reservists on stand-by amid speculation of a ground invasion.
After a lull overnight, Gaza City was hit by a series of large explosions just before dawn on Saturday.
Militants in Gaza have continued to fire rockets into Israel, aiming at Tel Aviv and Jerusalem on Friday.
At least 29 Palestinians and three Israelis have died since Israel killed Hamas's military chief on Wednesday.
In a telephone call with Israeli Prime Minister Benjamin Netanyahu, US President Barack Obama repeated his country's support for Israel's "right to defend itself".
A White House spokesman said the two men also discussed options for "de-escalating the situation".
Gaza City: Tweeting violence
Rocket took off less than half a kilometre from our office in #Gaza. It was huge so we are bracing ourselves for an #Israeli response.”
Mr Obama also spoke to Egyptian President Mohammed Mursi on Friday, praising his efforts to pacify the situation in Gaza, added the spokesman.
Your stories: Israel and Gaza
End Quote Muhammad Abu Shaban, Gaza City
When the F16s fly low, it's like a monster chasing its victim”
End Quote Hen Kinan, Beersheba, Israel
It was terrifying for my nieces and nephews”
On Friday, Israeli army spokesman Yoav Mordechai said: "Tonight won't be calm in Gaza."
Overnight, the area had been quiet but for the almost-constant buzz of drones overhead until, shortly after 03:30 (01:30GMT), the intensity of the air strikes increased.
There was another series of strikes in and around Gaza City shortly after 05:00, with several reportedly targeting Hamas' main government buildings.
The BBC's Jon Donnison tweeted: "Five big air strikes now shaking my room. Feels close."
Israel's military said it had targeted 180 sites since midnight.
Rumours have been swirling that a ground attack is imminent, but Israeli officials say no decision has been made.
Israel blocked access to three major routes leading into Gaza on Friday; call-up papers have already been sent to 16,000 Israeli reservists, with officials authorising the mobilisation of another 75,000.
Militants and civilians, including at least seven children, have been among the Palestinians killed during the two-day Israeli bombardment, Hamas says.
Hamas's military leader Ahmed Jabari was killed by an Israeli air strike on Wednesday. A senior commander was killed on Friday, officials said.Tel Aviv targeted
Before the recent offensive, Israel had repeatedly carried out air strikes on Gaza, as Palestinian militants fired rockets across the border.
Two Israeli women and a man died when a rocket hit a building in the southern town of Kiryat Malachi on Thursday, Israeli officials said.
On Friday, a rocket landed in Gush Etzion, south of Jerusalem. Haaretz newspaper said it was the first time since 1970 that a rocket had been fired at Jerusalem.
It is not clear whether the rocket was the same Iranian-built Fajr-5 launched towards Tel Aviv for the second day on Friday.
The Fajr-5 has an estimated range of 75km (45 miles).
Analysts say it is the first time Gaza militants have deployed such powerful missiles.
Israel says its assault on Gaza is aimed at knocking out rocket-firing facilities.
A spokesman said on Friday it had destroyed Hamas's "nascent" unmanned aerial vehicles (UAV) programme.
Known for its wealthy high tech industry, its chic cafes and bars, Tel Aviv is viewed by much of the rest of Israel as a bit of a hedonistic bubble, but that bubble burst over the last couple of days when rockets from Gaza reached Tel Aviv for the first time.
Israel's powerful air force says it has been pounding Gaza's weapons depots and launch sites so the fact Gaza militants are still able to fire medium range missiles that reach as far as Tel Aviv and Jerusalem worries Israelis.
In Tel Aviv itself, most people seem to be simultaneously surprised, a little scared and overwhelmingly stoic.
Miriam, a barista in Tel Aviv's fashionable Shenkin Street said: "I expect rockets to fall in Israeli towns close to Gaza but not here in Tel Aviv. It's scary but I'm hopeful that in the end things will get better. I have to be hopeful. I have no choice."
Israel's army said on Friday that during the operation - codenamed Pillar of Defense - it had targeted "600 terror sites in Gaza, including underground rocket launchers & infrastructure".
It said 97 rockets fired from Gaza had hit Israel on Friday alone - 388 since Wednesday. Its radar defence system - Iron Dome - had intercepted 99 rockets.
Palestinian Authority President Mahmoud Abbas has accused Israel of carrying out "massacres".
Western leaders and UN Secretary General Ban Ki-moon have appealed for both sides to stop the escalation in violence.
Britain and Germany have both said Hamas bears the brunt of the blame and should stop firing rockets immediately.
But Egypt's President Mursi has called the Israeli raids "a blatant aggression against humanity" and promised that Egypt "will not leave Gaza on its own".
Ties between Hamas and Egypt have strengthened since Mr Mursi's election earlier this year.
Hamas was formed as an offshoot of the Muslim Brotherhood, to which Mr Mursi belongs.
Jabaliya refugee camp
A man surveys the rubble of a house in Jabaliya refugee camp
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Iron dome defensive system
1. Enemy fires missile or artillery shell
2. Projectile is identified and tracked by radar. Data is relayed to battle management and control unit
3. Data is analysed and target ting coordinates are sent to the missile firing unit
4. The missile is fired at the enemy projectile exploding nearby to destroy the munition