Israel has massed forces along the border with Gaza
Violence has continued in the Gaza Strip for a sixth day, after calls for a UN-backed ceasefire between Israel and Palestinian militants foundered.
A series of Israeli air strikes hit the parliament building and the justice ministry. There are reports of damage to a children's hospital.
Rockets fired by Hamas militants have again landed in Beersheba, some 40km (24 miles) inside Israel.
Israel on Wednesday rejected calls for a 48-hour truce to allow aid into Gaza.
A draft UN resolution put forward by Egypt and Libya failed after the US and UK complained that it called on Israel to ends its air assaults but made no mention of Hamas rocket attacks against Israel, which they say started the latest hostilities.
Since the Israeli air offensive began on Saturday, jets and attack helicopters have targeted Hamas security compounds, government buildings, smuggling tunnels under the border with Egypt and homes belonging to militant leaders.
Palestinian medical officials say 391 Palestinians have died in the Israeli air strikes; the UN says 25% of these were civilians.
Four Israelis have been killed by rockets fired from Gaza, which is under Hamas control.
Palestinians sources say Gaza's Justice Ministry, Legislative Assembly and Education ministry were hit.
A workshop and several money changers' officers were also hit, one of which was close to a children's hospital.
Israel said it targeted at least five smuggling tunnels along the border with Egypt, a weapons manufacturing and storage facility in central Gaza, and a Hamas police command centre in Rafah.
The UN's relief agency, Unwra, says Gaza is facing a dire humanitarian situation and is on the brink of catastrophe.
Spokesman Chris Gunness said food distribution had restarted to thousands of Palestinians, but the operation faced "huge and difficult problems".
The agency's Commissioner-General, Karen AbuZayd, said 20,000 people a day had been without food aid for two weeks.
"People are doing pretty badly," she told the BBC.
"We do see for the very first time people going through the rubbish dumps looking for things, people begging, which is quite a new phenomenon."
However, Capt Benjamin Rutland of the Israeli Defence Force told the BBC that enough food and medical supplies were getting through.
Despite the failure of the initial UN talks, diplomatic efforts continue to bring an end to the fighting.
France's President Nicolas Sarkozy has said he would visit the region on Monday, although he is not scheduled to travel to Gaza.
But Palestinian President Mahmoud Abbas has threatened to pull out of peace talks.
He called the Israeli bombardment of Gaza "barbaric and criminal aggression" and said he "would not hesitate to stop" peace talks with the Israelis "if they go against our interests and offer a support to aggression".
Future of the conflict
Israel and Hamas say they may consider a ceasefire in the future, but their terms are very different.
Israel wants a permanent end to Hamas rocket attacks, while Hamas wants the Israeli air strikes to stop and the blockade on Gaza to be lifted.
Opinion polls in Israel indicate strong public backing for the air campaign, but support for risky action on the ground is much lower.
However, Israeli Defence Minister Ehud Barak has spoken of "widening and deepening the operation".
The Haaretz newspaper reported on Thursday that the Israeli army had recommended a major but short-term ground offensive.
Israel has massed forces along the boundary with Gaza and has declared the area around it a "closed military zone", leading to speculation a ground offensive into the tiny coastal strip could be imminent.
International reporters have been barred from entering Gaza, however Israel's Supreme Court told the government to allow at least some foreign journalists to enter.
The government was given until Thursday morning to respond.