Israel has targeted the headquarters of Hamas leaders and other key facilities in Gaza, on the fourth day of Israeli air strikes in the territory.

Prime Minister Ismail Haniya's office, which Egypt's PM had visited on Friday, was among the buildings destroyed.

At least 39 Palestinians and three Israelis have died since Israel killed Hamas's military chief on Wednesday.

Israel earlier put 75,000 reservists on stand-by amid speculation of an impending ground invasion.