Gunmen linked to the Fatah party of Palestinian leader Mahmoud Abbas have paraded through Gaza City, defying a ban on displays of force.
The Fatah gunmen paraded through the streets and fired in the air
The Hamas-led government told militant groups to stay off the streets after three died in violence on Friday.
About 300 Fatah gunmen fired into the air and called for new Prime Minister Ismail Haniyeh to arrest the leader of a rival group blamed for the fighting.
Friday's fighting began when a car bomb killed a member of the rival group.
The Popular Resistance Committee (PRC) accused Mr Abbas of conspiring with Israel to kill Khalil al-Quqa.
But local Fatah leader Samir al-Mushrawi insisted that those accusations could not be allowed to stand.
Mr Mushrawi, one of Gaza's most powerful figures, said Hamas needed to exert its authority on a volatile situation.
"It seems that the brothers in Hamas forget that they are in power, and represent a Palestinian government and are responsible for defending security institutions," he told the Associated Press.
Plea for calm
For his part, Mr Haniyeh on Saturday repeated his call for calm, urging rival factions not to resort to violence.
"What happened was dangerous and must not be repeated," he said, adding that Palestinians would need time to adjust to a culture that does not resort to using arms and violence.
The show of strength highlighted the difficulties Hamas is expected to have controlling those fighters and security forces loyal to Fatah.
The BBC's Alan Johnston, in Gaza, says there are questions as to how effectively Hamas will be able to control the various security agencies.
In the past, they have tended to be loyal to the Fatah political party, which Hamas has just ousted from power.
Security forces told Hamas on Saturday that they were investigating Friday's violence, in which three died and some 20 people were injured.