Gunmen have killed at least 13 people in the latest factional violence in the Gaza Strip, ending a third attempt at a ceasefire in as many days.
Abu Shbak's house was stormed by 200 Hamas gunmen, Fatah said
A dawn raid on the home of a top Fatah official left five people dead, only hours after the truce was agreed by the feuding Hamas and Fatah factions.
Later Hamas gunmen ambushed a jeep and mistakenly killed five fighters from their own side detained by Fatah men.
Some 40 people have died since fierce fighting broke out in Gaza on Sunday.
Two members of the pro-Fatah Preventive Security force and a bystander were also killed in the ambush, in the centre of Gaza City.
Separately, Hamas militants fired barrages of rockets at Israeli towns, in what correspondent said was an apparent attempt to draw Israel into the internal Palestinian conflict.
An Israeli aircraft bombed a Hamas training camp in southern Gaza in apparent retaliation, witnesses said. Details are still coming in.
The violence is the worst since February, when Hamas and Fatah agreed to form a national unity government.
Officials said Palestinian Authority President Mahmoud Abbas, of Fatah, spoke with exiled Hamas political chief Khalid Meshaal, and they agreed on the necessity of ending the fighting.
A senior Fatah official, deputy Prime Minister Azzam Ahmad, urged Mr Abbas to declare an emergency in Gaza, allowing him to rule by decree.
The BBC's Aleem Maqbool, in the West Bank town of Ramallah, says that whatever the militants started fighting for, the killings are now in the name of revenge.
The streets of central Gaza City were empty except for masked gunmen, as the air rattled with gunfire, eyewitnesses said.
Electricity to some areas was cut off forcing terrified residents to huddle in darkness in their homes.
The latest Egyptian-brokered ceasefire was declared late Tuesday night but failed to take hold.
Within hours, grenades were thrown at a Hamas security force post, reports said, followed by mortar fire targeting the office of Palestinian and Fatah leader Mahmoud Abbas.
The most deadly attack then followed, as some 200 Hamas gunmen surrounded and attacked the home of Rashid Abu Shbak, a Fatah chief who controls three Palestinian security forces, Fatah said.
Part of the house was burned down, and at least five security guards were killed, although Rashid Abu Shbak was not at home at the time, Palestinian security officials and Fatah sources said.
On Tuesday at least 14 people died in an attack on a Fatah military training base near the Karni crossing point with Israel.