Fatah ordered its security forces into the streets to defend against what it is calling a "coup." At least 22 people were killed and 70 wounded in the violence Tuesday, hospital officials told Reuters.
The clashes followed fighting in which at least 14 people were killed Monday, including a Hamas cleric gunned down in front of a mosque, two men thrown off high-rise buildings, and a Fatah militant shot 40 times outside his home. Also, the homes of both President Mahmoud Abbas of Fatah and Prime Minister Ismail Haniyeh of Hamas were fired upon, in what Haniyeh called an assassination attempt.
"I think we are in Iraq, not Gaza," 40-year-old taxi driver Tamer Ammar told Reuters. "Snipers on rooftops killing people. Bodies mutilated and dumped in the streets in very humiliating ways. Houses bombarded and civilians killed. What else does civil war mean but this?"
More than 630 Palestinians have died in factional fighting since March 2006, when the Islamic Hamas party came to power by defeating the secular Fatah party in parliamentary elections.
In March, the two parties formed a unity government led by Abbas and Haniyeh in an attempt to stop the fighting.
However, the unity government has generally been unable to keep the violence under control, with clashes in May leaving at least 50 dead. Hamas and Fatah have repeatedly negotiated short-lived truces, including a quickly abandoned one brokered by Egypt Monday.
On Tuesday, Hamas' armed wing issued an ultimatum giving Fatah security forces until 2 p.m. to evacuate security headquarters in Gaza City. When the deadline passed, Hamas fighters attacked the compound.
Fatah leaders were meeting Tuesday evening to discuss leaving the unity government coalition. Both Abbas and Haniyeh have called for restraint and talks, but their followers have not heeded those calls.
Israeli Prime Minister Ehud Olmert for the first time expressed support for the idea of stationing international peacekeepers in Gaza Tuesday, saying the idea should be given "serious consideration." Israel has long opposed such a move, saying that it would interfere with its security measures there.
"If the Gaza Strip ultimately falls into the hands of Hamas, it will have regional significance," Olmert said in a statement Tuesday.
Last week, the Jerusalem Post reported that Israel was considering allowing Egypt to supply arms to Fatah loyalists in Gaza.
Meanwhile, the European Union said that there was a risk of "imminent civil war" and U.N. Secretary-General Ban Ki-moon urged support for Abbas' efforts to restore law and order.