Hamas officials said an explosion went off early Thursday near a group of Hamas policemen patrolling in Gaza City , wounding three, including one critically.
Hamas blamed the rival Fatah movement for the attack, and said it has rounded up several suspects.
The explosion came at a time of rising tensions between the bitter rivals.
Earlier this week, Hamas blamed Fatah for what it said was a failed attack on a Hamas security compound. In the incident, three Fatah activists and a bystander were killed when a blast went off in a car, possibly because of mishandled explosives. A day later, Hamas raided a four-story Fatah office building.
Hamas took control of Gaza by force in June, defeating the security forces loyal to Fatah and moderate Palestinian President Mahmoud Abbas.