Hamas government buildings in the Gaza Strip have been flattened by continuing Israeli air strikes.
The attacks began on Saturday morning and are now in their third day.
Palestinian medical officials said on Monday the toll has risen to 327 dead and around 700 wounded.
Israeli warplanes bombed the Interior Ministry on Monday. The ministry supervises the group's security forces. The building had been evacuated and there were no casualties.
The homes of two top commanders of the armed wing of Hamas were also attacked. Several family members were reported among the dead.
Israeli military commentators say the army is reinforcing its forces for a possible ground incursion.
Hamas took over the Gaza Strip in 2007 and ended a truce on 19 December.
Israel has declared areas around the Gaza Strip a "closed military zone".
The attacks are in retaliation for continuing rocket attacks which have intensified since the end of the truce.
Israeli defence minister Ehud Barak says Israel is involved in an "all-out war" against Hamas and its leadership.
Mr Barak told the Israeli parliament on Monday that the goal of the current military operation was to stop Hamas attacking Israeli civilians and soldiers - a reference to Palestinian rocket fire from Gaza.
An election is due to be held in Israel on 10 February.