Hamas fighters hunted down key loyalists of the Palestinian president Mahmoud Abbas in the Gaza Strip today after seizing most of the final Fatah strongholds.
Palestinian demonstrators try to convince Fatah militants to stop shooting during clashes with Hamas militants
In the West Bank, Mr Abbas reacted by signing decrees dismissing the three-month-old unity government formed with Hamas led by Prime Minister Ismail Haniyeh and declaring a state of emergency.
But legal moves seemed overtaken by the violence.
Hamas said it "executed" a top Fatah "collaborator" and it issued a death list of other key supporters of President Abbas.
Jubilant young Hamas gunmen hoisted green Islamist flags over captured Fatah buildings and pounded remaining Fatah bastions, including Mr Abbas's Gaza base, with heavy weaponry.
The White House accused them of "acts of terror" and urged Arab governments to rally behind Mr Abbas and the "moderates".
Israel and its allies contemplated the emergence of an aggressive, Islamist "Hamastan" on its border and a split between Gaza and the larger West Bank, controlled by Fatah.
At least 29 more people were killed in Gaza, hospital staff said, including 18 Fatah men found in the headquarters of Mr Abbas's Preventive Security force. The rout earlier today prompted Hamas to declare the "liberation" of Gaza.
In all, at least 110 people have been killed in six days of fighting that many of Gaza's impoverished 1.5 million people regarded as a civil war.
Since Hamas won the general election in March a crippling cash and aid embargo was imposed by Israel and Western powers.
Casualty figures are unclear, as was the fate of Fatah fighters seen led away, bare-chested, after surrendering. There were unconfirmed reports of prisoners being shot.
A Fatah official in Gaza said he had seen eight colleagues gunned down while he escaped death "by a miracle".
Hamas's armed wing issued a statement saying it had "executed" Samih al-Madhoun of Fatah's al-Aqsa Martyrs Brigades, a close ally of Mr Abbas's top security aide Mohammad Dahlan.
Some Fatah gunmen retaliated in the West Bank, shooting and wounding a Hamas man near Ramallah, seizing Hamas supporters in the towns of Jenin and in Nablus, where they also stormed a Hamas office.
Even businesses owned by Hamas supporters were targeted by angry crowds in the territory occupied by Israel, where some 2.5 million Palestinians live, in the hills around Jerusalem.
Mr Abbas signed three decrees, aides said. One dissolves the Hamas-led "unity government" that Fatah joined in March under a Saudi-brokered deal aimed at ending internal violence and easing Western sanctions for Hamas's refusal to recognise Israel.
A second decree establishes a state of emergency and a third establishes an "emergency" government, officials said.
Israeli Prime Minister Ehud Olmert has said an international force along Gaza's border with Egypt should be considered. But despite some international murmurs, putting such a force together against Hamas's wishes seems unlikely for now.
Meanwhile, four young Palestinians died in an explosion in southern Gaza. The Israeli army was checking reports from residents that they were killed by an Israeli tank shell.
Hospital officials said the four, all aged under 18, had been killed by a shell fired in the town of Rafah near the border with Egypt. Palestinian residents said Israeli troops had been operating in the area.
Agencies