Since the launch of Israeli massive airstrikes on Gaza on Saturday in response to rocket and mortar fire by Hamas militants on southern Israel, 277 Palestinians are reported to have been killed.
The Seraya security compound in Gaza City bombed by Israel includes the headquarters of several Hamas security structures, and also two prisons.
Hamas seized control of the Gaza Strip from President Mahmoud Abbas's Fatah group in June 2007.
Meanwhile, Israel is mobilizing some military reservists for a possible ground operation in the Gaza Strip, local television reported.
Israel's Ynet web portal and the Israeli newspaper Jerusalem Post reported on Sunday that the Israeli army was pulling tanks and infantry reinforcements close to Gaza.
Ynet referred to Israeli Defense Minister Ehud Barak as saying in an interview with British Sky News television that the Israeli ground forces would enter the Gaza Strip, if the move was deemed necessary by Jerusalem.