Two people have been killed in clashes overnight between gunmen from the Palestinian groups Hamas and Islamic Jihad, reports from the Gaza Strip say.
Hamas has pledged to bring security to the streets of the Gaza Strip
The incident follows clashes on Wednesday in which one Hamas fighter died and several others were injured.
Hamas says the clashes come after its men tried to detain Islamic Jihad men violating a ban on celebratory gunfire.
Hamas banned such gunfire, at weddings and funerals, after it seized control of the Gaza Strip last month.
Correspondents say the incidents are an indication of the growing animosity between the two Islamist groups, Hamas and Islamic Jihad, now that their common enemy, the secular Fatah has been vanquished in Gaza.
One of those killed on Thursday was reportedly from Islamic Jihad. A second man from Fatah, was also killed, although it is not clear how he became involved.
Islamic Jihad described Thursday's violence as an ambush.
It says its men were dragged out of a mosque and shot in the legs by Hamas gunmen.
Witnesses said Fatah official Salah Amoudi was shot dead by masked gunmen shortly afterwards, on his way home from the mosque.
The Hamas-run interior ministry issued a statement pledging "not to hesitate with anyone violating the law and trying to sabotage the stability in Gaza".
It said the circumstances of Mr Amoud's death were being investigated.