Israeli air strikes today destroyed a Hamas security headquarters and a car carrying one of the Islamist group's top commanders in a powerful response to rocket attacks by Palestinian militants.
At least one Hamas militant was killed and more than 40 others were wounded in two air strikes.
Smoke rose from what remained of the downtown office building that housed Hamas's Executive Force, which has been locked in fierce street battles for six days with fighters loyal to President Mahmoud Abbas's secular Fatah faction.
About two hours later, an Israeli air strike on a car killed at least one Hamas militant. The vehicle was also carrying a senior commander in Hamas's armed wing. Ambulance crews said he was critically wounded.
Despite a ceasefire deal brokered by Abbas and Hamas leader-in-exile Khaled Meshaal, three Palestinians were killed in renewed internal fighting today, raising the death toll since Friday to at least 43.
Hamas's armed wing threatened to resume suicide bombings in Israel after the Gaza attack levelled the Executive Force's multi-storey concrete structure. A Hamas bomber last struck in Israel in 2004.
Hamas accused Israel of doing Abbas's bidding by attacking the facility and other installations used by the militant group.
The Israeli army has denied its attacks were connected to the factional violence, which has brought Palestinians to the verge of all-out civil war.
Meshaal told Hamas's al-Aqsa Television that the air strike in Gaza City created an "historic opportunity" to unite Palestinian factions against Israel.
Hospital officials said at least 40 people were wounded in the attack on the Executive Force facility. Witnesses said people were still trapped under the collapsed multi-storey structure.
"We have had enough. Israel will take all defensive measures to protect our citizens from these Hamas rockets," Miri Eisin, a spokeswoman for Israeli Prime Minister Ehud Olmert, said before the air strike.
At least two Israelis were lightly wounded by rocket salvoes in the southern town of Sderot, near the Gaza border.
The Gaza violence has worsened conditions for Palestinians hard hit by Western sanctions against the Hamas-led government. Olmert has ruled out serious peace talks so long as the government refuses to recognise Israel and renounce violence.