GAZA (Reuters) - In what looked ever more like civil war, the forces of Palestinian President Mahmoud Abbas battled supporters of the Islamist prime minister across Gaza on Tuesday, the bloodiest day of factional fighting in months.
At least 27 people were killed and 70 wounded, hospital officials said, taking to 47 the number of dead in the coastal enclave since Saturday. Early on Tuesday, the Gaza homes of both Abbas and Prime Minister Ismail Haniyeh of Hamas were fired on.
The largest force loyal to Abbas, who is favored by Western powers, was ordered onto the streets to defeat what his secular Fatah group called a "bloody coup" by Hamas Islamists after Hamas gunmen stormed Fatah bases in the Gaza Strip.
Hamas later appeared to have control of one major Fatah base in the north and casualty data suggested it had the upper hand more widely. Fatah leaders threatened to quit a three-month-old unity government with Hamas if there was no immediate truce.
The European Union said there was an imminent risk of civil war if fighting went on, and U.N. Secretary General Ban Ki-moon urged support for Abbas's efforts "to restore law and order".
Haniyeh and Abbas both called for restraint and talks but, as each side accused the other of siding with their Israeli adversaries, there was little sign of fighters paying heed.
The head of an Egyptian delegation in Gaza that saw its latest truce shot down on Monday, urged civilians to rally on Wednesday morning to show support for a new ceasefire.
Israeli Prime Minister Ehud Olmert, an arch-foe of Hamas, said for the first time that "serious consideration" must be given to posting international peacekeepers in Gaza, from which Israel withdrew troops and Jewish settlers two years ago.
"If the Gaza Strip ultimately falls to Hamas, this will be of great regional significance," he said, but added Israel could not enter Gaza to fight Hamas to help Abbas's "pragmatists".
Hamas gunmen swept down on Fatah posts, residents said. At one stage, Hamas fighters gave Fatah forces half an hour to evacuate bases -- an unprecedented ultimatum.
Intense gunfire and explosions were later heard from a base of Abbas's National Security Forces in Gaza City. Reinforcements for the NSF moved in vehicles through the deserted streets.
"Advance!" NSF commanders ordered, as Hamas radio stations were briefly jammed by music praising Fatah military leaders.
"Confront the seekers of the coup!"
At least 16 people were killed in ensuing evening battles, according to hospital officials -- including 11 in one clash that Hamas said gave it control of a major NSF base in the north of the Strip. Hamas officials said they lost at least nine men while Fatah sources said their losses were at least 16 dead.
Abbas, successor to Yasser Arafat, convened Fatah's Central Committee in his West Bank base. It issued a statement saying: "The Central Committee decided that its ministers will not participate in the government if there is no ceasefire now."
If they resign, along with some independent ministers, Abbas could fire the government and try to rule by decree. A new cabinet would need approval from the Hamas-led parliament.
Most of the Gaza Strip's 1.5 million inhabitants took refuge in their homes. Crammed into a 45 km (27 mile) sliver of coast and surrounded by an Israeli security cordon, they have little chance to flee through the restricted main crossing into Egypt.
"I think we are in Iraq, not in Gaza," Ammar, a 40-year-old father of six, said. "Snipers on rooftops killing people. Bodies mutilated and dumped in the streets in very humiliating ways.
"What else does civil war mean but this?"
Since Hamas won an election in January 2006, boosted by its support among the poor of Gaza, more than 600 Palestinians have been killed in factional fighting, according to one estimate.
After some months of relative calm, fighting flared up again last month before easing following a truce brokered by Egypt.
The United States has been helping train and arm Abbas's forces, citing the Fatah leader as a moderate committed to peace and a counterweight to Hamas, which has ties to Iran and Syria.
Additional reporting by Mohammed Assadi and Ali Sawafta in Ramallah and Adam Entous, Jeffrey Heller, Ori Lewis and Alastair Macdonald in Jerusalem