Ongoing fighting
Hamas security forces had demanded the clan surrender members who were involved in clashes on Wednesday in which at least three Palestinians were killed.
Mediators from other Palestinian factions said they had brokered a ceasefire agreement, but witnesses said parts of Gaza City were still closed off and that fighters were roaming the streets.
"Since last night the members of the Hellis family have shown they have no intention of implementing our agreement and have erected sand blockades, laid mines and taken up arms," said Ihad al-Ghussein, a spokesman for the Hamas's interior ministry.
Wednesday's clash was one of the biggest since Hamas took over the Gaza Strip after defeating Abbas's forces after heavy fighting in June.