Palestinian gunmen ambushed a judge from the ruling Islamic militant group Hamas as he arrived at a courthouse in Gaza.
Witnesses say Bassam al-Fara was dragged from a taxi and shot dead. Al-Fara was also a senior commander of the Hamas military wing.
Hamas blamed the rival Fatah faction for killing the judge and promised revenge. It was the latest in a wave of attacks between the two groups that has raised fears of a Palestinian civil war.
The ambush came two days after the targeted killing of three young children of a commander from Fatah who was seen as an enemy of Hamas.
The violence is part of a deepening struggle between moderate Palestinian President Mahmoud Abbas and the Hamas-led government. Palestinian analyst Bassam Eid says the people are fed up with both of them and with the lawlessness on the streets.
"I think that most of the Palestinians now becomes much more hopeless, much more pessimistic towards the government, towards the Palestinian President, in term to put an end for such a huge chaos."
Following the attack on the judge, more than a thousand Fatah police and gunmen blocked roads and fired in the air.
They marched to the office of President Abbas, demanding that he sack the Hamas government over the collapse of law and order.