Palestinian President Mahmoud Abbas ordered security forces to deploy across Gaza today after the killing of three young sons of one of his loyalists.
Tension between Mr Abbas and Hamas soared after the attack by unidentified gunmen yesterday. The three children of a senior intelligence chief were shot dead as they arrived at school.
Early today, heavily armed members of those security forces that take their orders from Mr Abbas took up positions around key installations and road junctions in Gaza City.
A force loyal to the Hamas government also strengthened its positions. There was no immediate sign of friction between the Abbas and Hamas loyalists, but fear of fresh clashes deepened sharply yesterday.
It was the first time that children have been targeted in such an attack. Angry mourners firing guns stormed the parliament compound during the funeral for the boys, aged six to nine.
A senior Palestinian intelligence official in the occupied West Bank said it was unclear who was behind the attack on Colonel Baha Balousha's children.
Besides internal political unrest, Gaza is riven with clan fighting and a surge in crime following a Western aid embargo on the Hamas government that has deepened poverty.
Political tension has been rising over the failure of Hamas and the formerly dominant Fatah movement to form a unity government that Palestinians hope might end the Western boycott.
Aides to Mr Abbas said on Saturday the president planned to call early elections after talks on a unity government foundered. Hamas accused Mr Abbas of trying to topple the government, which came to power after winning elections.