The Palestinian Foreign Ministry was bombed by Israeli aircraft for the second time in a week, injuring five residents.
An 8-story section of the building collapsed and dozens of houses were damaged in the area.
Five residents were taken to the local hospital.The ministry was thought to be empty at the time.
An Associated Press reporter at the scene saw clouds of smoke rising from the damaged building.
Israeli army officials refused to comment.
This is the second attack on the ministry in a week after Israel bombed the same building Thursday saying that it was used by Hamas operatives to plan terrorist attacks.
The Palestinian foreign minister is Mahmoud Zahar, a Hamas leader.
The Israeli army also bombed the north Gaza offices of a Hamas-led security force before dawn Monday, witnesses said.
The building, in the Jebaliya refugee camp, caught fire though there were no reports of injuries.