Fearful that Hamas' momentum could spread to the West Bank, Fatah went on the offensive there, rounding up three dozen Hamas fighters. Angry militants threw office furniture out a third-story window of the Palestinian parliament building in Ramallah, then set fire to the office of three Hamas lawmakers.
A Hamas activist was shot and killed in Nablus, the first person to be killed in the West Bank after days of violence in Gaza; the Al Aqsa Martyrs' Brigades, a violent Fatah offshoot, claimed responsibility.
It was a day of major victories for Hamas and its backers in Iran and Syria — and of devastating setbacks for the Western-backed Fatah.
On TV, Hamas publicly humiliated its enemies, showing the capture of Fatah holdouts, reports CBS News correspondent Richard Roth.
In one particularly humiliating scene, masked Hamas fighters marched agents of the once-feared Preventive Security Service out of their headquarters, arms raised in the air, stripped to the waist and ducking at the sound of a gunshot.
What Hamas didn't broadcast were the brutal streetside executions, adds Roth.
Witnesses, Fatah officials and a doctor reported executions by Hamas militants of defeated Fatah fighters; Fatah said seven of its men were shot in the head, gangland-style. Hamas denied any such killings.
The violence has killed at least 90 people in the past five days, including 33 on Thursday alone.
Abbas, of Fatah, fired the Hamas Prime Minister Ismail Haniyeh and said he would install a new government, replacing the Hamas-Fatah coalition formed just three months ago. Abbas' decrees won't reverse the Hamas takeover of Gaza. Instead, his moves will enable Fatah to consolidate its control over the West Bank, likely paving the way for two separate Palestinian governments.
Haniyeh said that Abbas' decision to fire him and his government over Gaza violence was "hasty." Haniyeh told a late-night Gaza news conference that Abbas and his advisers did not consider "the consequences (of the decision) and its effects on the situation on the ground."
Because Fatah has recognized Israel's right to exist and signed on to past peace agreements, the international community's boycott of the Palestinian territories in the wake of Hamas' electoral successes may no longer apply to the West Bank, just to Gaza. Some 2 million Palestinians live in the West Bank, while 1.4 million reside in Gaza.
Hamas' success has thrown into turmoil everything from Mideast peacemaking to Palestinian statehood to relations with Israel and the West.
"The era of justice and Islamic rule has arrived," Hamas spokesman Islam Shahawan said.
Fatah's old demons — corruption, petty quarreling, lack of leadership — led to its dismal performance. While disciplined Hamas systematically hoarded weapons, Fatah's Gaza leader, Mohammed Dahlan, preferred travel and West Bank politics to preparing for the inevitable showdown with its rival. Dahlan returned Thursday from Egypt, where he stayed several weeks after knee surgery. But instead of going to Gaza, he headed for Ramallah.
In other developments:
Many West Bank Palestinians, watching the fall of Gaza on their TV screens, pinned the blame on Abbas, whom they see as indecisive and detached. During Hamas' assaults in Gaza this week, no prominent Fatah leader was in the coastal strip to take command.
"Hamas has leadership, a goal, an ideology and funding," said Gaza analyst Talal Okal. "Fatah has neither leadership, nor a goal, a vision or money."
By capturing Gaza City's three main security compounds and the southern town of Rafah, Hamas secured its hegemony in Gaza, putting Islamic extremists in control there. Hamas seized its final target, Abbas' Gaza City headquarters, late Thursday, according to witnesses.
For first time since fighting erupted five days ago, Abbas issued an order to strike back. But his words were too little, too late.
Hamas spokesman Sami Abu Zuhri said Abbas' decisions have "no value" on the ground.
This week's fighting has been the most intense since Hamas won parliamentary elections last year, setting the stage for a violent power struggle with Fatah. Hamas reluctantly brought Fatah into the coalition in March to quell an earlier round of violence, but the uneasy partnership began crumbling last month over control of the powerful security forces.
No battle was more indicative of Gaza's hatreds and passions than the one at Preventive Security, one of Fatah's four main security bases in the coastal strip. After Hamas fighters overran it in a hail of mortar and gunfire Thursday, they touched their heads to the ground in prayer and marched vanquished gunmen into the streets shirtless.
Preventive Security carried out a brutal crackdown on Hamas in 1996, and the militants never forgot it. "There is a history to it, a vendetta and a settling of scores," said Palestinian lawmaker Hanan Ashrawi.
Fatah officials, speaking on condition of anonymity for fear of retribution, said Hamas shot dead seven Fatah fighters after they had surrendered. A doctor at Shifa Hospital said he examined two bodies that had been shot in the head at close range.
A witness named Amjad who lives in a high-rise building that overlooks the Preventive Security complex said men were killed in front of their wives and children.
"They are executing them one by one," Amjad said in a telephone interview, declining to give his full name for fear of reprisals. "They are carrying one of them on their shoulders, putting him on a sand dune, turning him around and shooting."
The killers, he said, ignored appeals from neighborhood residents to spare the men's lives.
Abu Zuhri, the Hamas spokesman, denied the reports of gangland-style killings. "Whoever was killed was killed in clashes," he said.
Hamas TV said the Preventive Security building would be turned into an Islamic college. It showed a room with wall-to-wall wiretapping equipment, a testament to Fatah's collapsed control.
Hamas fighters later seized the Fatah-controlled intelligence services building, planting the Islamic group's green flag on the roof of the ship-shaped structure. And after nightfall, the group announced it had seized Fatah's last stronghold in Gaza, the National Security headquarters.
Hamas TV showed smoke billowing from the top two floors of the mortar-pocked, five-story intelligence building. Five masked gunmen posed inside for the TV camera, including one who raised two assault rifles in triumph.
Another gunman, wearing a Hamas headband around his helmet, stood in a pose of prayer, a hand to each side of his head, screaming "Allah is Great" at the top of his voice.
Spent bullets lay on the floor in one office, and a carton holding hand grenades stood in another area.
Outside the building, three masked gunmen prayed on the sidewalk, their weapons on the ground in front of them as they kneeled in prayer.