As up to 75,000 Israeli reservists were mobilised for a possible ground invasion, war planes made overnight raids on a series of government buildings and security installations. As well as Mr Haniyeh's offices, they hit the Hamas interior ministry and the massive police headquarters in Gaza City, which sparked a huge blaze that engulfed nearby houses.
Weapons storage facilities and underground rocket launching sites were also hit, as too were the vast network of smuggling tunnels used to bring in weapons and other contraband from neighbouring Egypt.
The new attacks followed an unprecedented rocket strike aimed at the holy city of Jerusalem on Friday, the first time Palestinian militants had targeted it in decades.
Six people, including five militants, were killed and dozens were wounded in the various attacks on Saturday, according to Ashraf al-Kidra, a Gaza health official.
The latest missile exchanges came amid signs of an imminent ground invasion. Commanders have hinted that it could possibly begin as soon as this weekend. Israel's armed forces have cordoned off a highway and two roads bordering the Gaza enclave, declaring it for military traffic only. Tanks and self-propelled guns were seen near the border area on Friday.
According to officials in Gaza, 38 Palestinians, half of them civilians including eight children and a pregnant woman, have now been killed in Gaza since Israel began its air strikes.
A three-storey house belonging to a senior Hamas official, Abu Hassan Salah, was also hit on Saturday and completely destroyed. Rescuers said at least 30 people were pulled from the rubble. Militants responded to the overnight airstrikes by firing dawn salvoes into Israel, but the number was notably lower than on the previous three days of the offensive, Israeli commanders claimed.
On Friday night, the Israeli Prime Minister, Benjamin Netanyahu, was locked in a strategy meeting with key advisors and ministers in Tel Aviv to discuss whether to widen the military campaign. No decision has yet been made, but the Israeli government has stressed that all options are open.
Despite the violence, Tunisia's foreign minister arrived in the coastal enclave early on Saturday in a show of Arab solidarity, heading to a hospital to visit the wounded.
By Colin Freeman Telegraph.co.uk