Hamas members have beaten protesters rallying in Gaza City, reports say.
Protesters said the ban by Hamas was "illegal"
Baton-wielding Hamas security forces tried to disperse the protesters from rival Palestinian factions, gathered to denounce the Islamist group.
Hamas - who seized the Gaza Strip in June - said organisers did not have a permit to hold a rally, violating a new ban on unauthorised public gatherings.
However, a number of people defied the ban and continued the rally, chanting "we want freedom".
"Hamas! What is happening in Gaza is not acceptable!" the demonstrators chanted, according to AFP news agency.
Hamas took over the Gaza Strip in mid-June
Among the protesters were members of Palestinian leader Mahmoud Abbas' Fatah faction.
Fatah said Hamas' actions amounted to the imposition of military rule in the Gaza Strip.
Reports say Hamas forces used clubs and rifle butts to beat demonstrators, confiscating cameras and videotapes used by journalists who had covered the rally.
Hamas banned unauthorised public meetings on Sunday, saying the measure was in the interests of public safety.
The group rejected claims that it was targeting its political rivals.
"There is no decision to ban rallies by Fatah or others," Ehab al-Ghsain, spokesman of the Hamas-run interior ministry, told Reuters news agency.
"Today's rally was stopped because organisers refused to seek permission," he said.