Israel has attacked the Palestinian prime minister's Gaza City office as it ratchets up the pressure over its captured soldier.
The Gaza City offices were hit by two Israeli missiles
The HQ was left in flames by the latest in a string of air raids and incursions carried out by Israel since Wednesday.
Israeli PM Ehud Olmert was meeting his cabinet on Sunday to decide what steps to take next in the crisis.
Israel says the military action will go on until Cpl Gilad Shalit, captured by militants a week ago, is freed.
"We will strike and will continue to strike at [Hamas's] institutions," said Interior Minister Roni Bar-On.
"They have to understand that we will not continue to let them run amok."
Other strikes overnight on Saturday hit a school in Gaza City and Hamas bases in northern Gaza, killing a 34-year-old militant.
Palestinian PM Ismail Haniya said the attack on his office, which injured three security guards, was senseless.
"They have targeted a symbol for the Palestinian people," he said, inspecting his burning office.
He met Palestinian Authority President Mahmoud Abbas for an hour after the attack, which came a day after the interior ministry was targeted.
Mr Abbas was also due to have talks on Sunday with UN envoy Alvaro de Soto, as diplomatic efforts to defuse the crisis continue.
Speaking before the latest strikes, Mr Abbas said he was still hopeful of a peaceful resolution, and the door to an agreement had not been closed.
As the military pressure continues, Israel reopened its main commercial crossing into Gaza on Sunday to allow fuel and other key supplies to be taken into the strip.
GAZA CRISIS TIMELINE
Sun 25 June: Cpl Gilad Shalit captured in cross-border attack
Mon 26 June: Palestinian Popular Resistance Committees demand prisoner releases in exchange for Shalit
Weds 28 June: Israeli military enters southern strip after launching air strikes on Gaza
Thurs 29 June: Israel detains dozens of Hamas officials
Sat 1 July: Groups believed to be holding Cpl Shalit demand 1,000 prisoners be released
The Karni crossing - shut after Cpl Shalit's capture - would be open six hours a day for four days this week, an Israeli official told AP news agency.
The Israeli air strikes have knocked out Gaza's only power station, leaving only limited electricity supplies and shrinking fuel stocks.
Some groups have warned of a looming humanitarian crisis for the civilian population.
Mr Olmert said fuel, essential goods and humanitarian aid would be allowed through the Karni crossing.
The three groups believed to be holding Cpl Shalit have demanded the release of 1,000 prisoners held in Israeli prisons, and an end to the Israeli offensive. Israel has rejected the demands.
Egyptian mediators have so far failed to secure the soldier's release.
Cpl Shalit, a tank gunner, was seized in a raid on his border post last Sunday in which two other soldiers and two of the attackers died.
A large Israeli force remains poised on Gaza's northern edge.
Casualties in Gaza have been relatively light since the incursion began, with the deaths of two militants reported before Sunday's air strikes.