At least four Palestinians have been killed and nearly 20 hurt in the Gaza Strip in fresh violence between backers of the rival Hamas and Fatah factions.
Hamas militants were involved in a fierce clash with a family in the southern town of Khan Younis.
Hamas blames the family for killing one of its commanders on Friday.
It is the first serious violence since Hamas and Fatah agreed to form a unity government three weeks ago, a BBC correspondent says.
Hamas said it was targeting those who executed their commander, and called on the Fatah movement to stay out of the fight, according to the BBC's Alan Johnston in Gaza.
Official Fatah units did not get involved in the fighting that lasted several hours, our correspondent says.
Meanwhile, the parliamentary speaker Ahmed Baher told a news conference that Hamas expected to form a coalition government with Fatah "by the first week of March".
Hamas and Fatah struck a major deal three weeks ago under which they agreed to end months of violence between them and go into government together.
The Hamas commander was stopped in Khan Younis late on Friday. He was then ordered out and shot in the street in front of his wife and children, our correspondent says.
Alan Johnston says that this looks like an act of revenge carried out by a family who suffered the loss of a relative, killed several months ago while he was serving in a force linked to the Fatah party.
There was always the danger that families on either side might continue to carry out revenge attacks that might undermine the new accord, our correspondent says.
He says that Palestinians will be very much hoping that the fresh violence in Khan Younis will be contained and brought under control before it can spread.
Factional fighting between Fatah and Hamas claimed more than 90 Palestinian lives since December.