Hamas security forces have arrested hundreds of rival Fatah members in the Gaza Strip, following a mass rally Monday that ended with seven people dead.
More than 200,000 people attended the Fatah rally on Monday that marked the third anniversary of the death of Palestinian leader and Fatah founder Yasser Arafat.
Fatah officials say Hamas took more than 400 Fatah members into custody.
Fatah accuses Hamas of opening fire on the crowd, killing the seven people. Hamas says it responded after its men came under attack by rival Fatah forces. Medical sources say some 100 people were wounded.
Palestinian President Mahmoud Abbas declared three days of mourning, beginning Tuesday.
Mohammed Dahlan, a senior Fatah leader who was forced to leave Gaza after the Hamas takeover in June, has called for more rallies to protest the rule of Hamas, saying ordinary Palestinians have had enough of the militant group.
Monday's rally was Fatah's biggest show of strength in Gaza since Hamas seized the territory in June, expelling the security forces of Mr. Abbas, who heads Fatah.
Some information for this report was provided by AFP, AP and Reuters.