A new outbreak of factional violence in Gaza has left at least 18 people dead in the past 24 hours.
Hamas militants have besieged two Fatah security headquarters in Gaza City and Jabaliya provoking clashes with those holed up inside.
Intense clashes have occurred at both locations, where hundreds of officers in the Fatah-linked Palestinian security force are based.
The fresh attacks come after mortar attacks on the homes of both Prime Minister Ismail Haniyeh of Hamas and President Mahmoud Abbas of Fatah last night.
Mr Abbas has called for a ceasefire and accused elements within Hamas of trying to seize power in Gaza by force.
An Irishman working as a senior United Nations official in Gaza has described the situation there as 'out of control'.
John Ging, who is head of the UN Relief and Works Agency in Gaza, said the ferocity of the violence was unprecedented.
The conflict threatens to topple the Hamas-Fatah coalition that took office less than three months ago in a bid to halt the feuding that has killed nearly 180 people since December.
Fatah has announced that the party's central committee is examining whether it should remain in government and criticised Hamas for 'looking to annihilate' the Palestinian Authority.
Overnight, more than 50 mortar shells were fired at the Gaza City headquarters of the Fatah security service and activists torched around a dozen homes of various Fatah and Hamas members.
