Israeli aircraft have launched an attack on Gaza City, hitting the office of the Palestinian Prime Minister Ismail Haniya.
The attack comes during an Israeli incursion into Gaza after one of their soldiers was abducted last week.
Witnesses said two missiles hit the south side of the offices of the Hamas-led cabinet, starting a fire.
Three security guards were reportedly injured in the attack, and at least one Hamas member died in a separate strike.
The attack on the cabinet offices took place at 0145 local time (2245 GMT). The prime minister was not there at the time.
Israel's defence forces (IDF) confirmed they had carried out an attack on Mr Haniya's office as well as two more Hamas sites in Gaza.
"The IDF will continue to employ all means at its disposal against Palestinian terrorist infrastructure in the Gaza Strip to allow the unconditional return of Corporal Gilad Shalit," a military spokeswoman said.
Mr Haniya visited the scene of the attack later, saying: "They have targeted a symbol for the Palestinian people."
"We ask the international community and the Arab League to take its responsibilities towards our people and intervene to bring an end to this aggression." He met Mr Abbas for an hour after the attack.
The BBC's Alan Johnston in Gaza says he heard the sound of helicopters, and that witnesses said one rocket struck Mr Haniya's second floor office, setting the building ablaze.
Another explosion was heard shortly after.
The attacks follow a strike on the office of the interior ministry on Thursday.
Our correspondent says the attacks on ministers' offices were a clear sign the Israelis regarded them as personally responsible for the soldier's fate.
Other strikes hit a school in Gaza City and Hamas bases in northern Gaza, killing a 34-year-old militant.
Israeli forces have also moved into the south of Gaza as part of efforts to free the soldier, Corporal Gilad Shalit, 19, captured by militants during a raid on an Israeli army post last week.
Speaking before the latest strikes, Palestinian leader Mahmoud Abbas said he was still hopeful of a peaceful resolution over the capture of the soldier.
He said that the door to an agreement had not been closed and that negotiations would continue but he indicated that there were limits to his optimism, said our correspondent.
The three groups believed to be holding the Israeli have demanded the release of 1,000 prisoners held in Israeli prisons, and an end to the offensive. Israel is refusing to consider a prisoner swap.
Egyptian mediators have so far failed to secure the soldier's release.
An official close to the negotiations told AFP news agency: "Our efforts to release the soldier have reached a dead end.
"We could not do any more to release him because there are too many demands interfering with our efforts."
The UN's special Middle East envoy, Alvaro de Soto, is expected to travel to Gaza on Sunday for talks with Mr Abbas.
Israel has rejected conditions set for information on, or the freeing of, the tank gunner who 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 as mediators make last-ditch attempts to reach a solution.
Israeli tanks and bulldozers crossing the border near Khan Younis ran into gunfire and grenades on Saturday.
It was the first sustained encounter between the two sides since the incursion was launched, our correspondent said.
However, casualties in Gaza have been relatively light since the incursion began, with the deaths of two militants reported before Sunday's air strikes.