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.
When General Wesley Clark spoke about the famous list of seven Middle Eastern countries to be demolished in five consecutive years, he has done nothing but remark, for the last time, if there was any need, Washington's willingness to redesign the Middle East within a more general framework of global domination.