Israeli helicopter gunships carried out four missile strikes against targets in Gaza city early on Sunday.
The is controversy over what the building is used for
The Israeli army said that the targets had been the offices of a militant group and on an area used to launch rocket attacks on Israel on Saturday.
Palestinian security officials said the missiles hit a charity belonging to the Islamic Jihad militant group.
There were no reports of casualties, though overnight five Palestinians died in inter-clan fighting in north Gaza.
Bloody clan clash
An Israeli army spokeswoman told AFP the air strikes, the first aimed at targets in the Gaza strip since 27 October, were "reprisals after the Palestinians fired Qassam rockets".
"One of these attacks targeted an office organising terrorist activities and three others targeted a sector in the north of the region from where Qassam rockets have been fired at Israel," she said.
After a lull of several weeks Palestinian militants fired three makeshift rockets at southern Israel from Gaza on Saturday.
The rockets reportedly fell near the Carmilla kibbutz, south of the town of Ashkelon and on the village of Nativ Ha Assera. No-one was reported injured in the attacks.
In other violence five Palestinians were killed and at least 10 hurt in a fire fight between two rival clans in the northern Gaza Strip, witnesses and medics said.
The two groups used assault rifles and grenades in the town of Beit Hanoun. One of those killed was a policeman.
It is a latest in a series of violent incidents since the Israeli pullout from Gaza in September.