(Breaking News Ireland) Four Hamas police officers were killed and two wounded tonight when a car exploded outside a Hamas security headquarters building in Gaza City, hospital and security officials said.
At first Hamas blamed Israel, but later said it was unclear what caused the blast.
The car exploded on the Gaza beachfront near the Hamas marine police force building.
The Hamas -controlled Gaza Interior Ministry released a statement saying the car was hit by an Israeli naval vessel offshore, killing four marine police officers.
But later, the Hamas government backed away, releasing a statement saying: "Investigations are still under way to determine what caused the blast, who was behind it and who was killed."
The Israeli military said it was not involved. Usually Israel takes credit for attacks on armed Palestinians, including frequent airstrikes .
Witnesses reported gunfire in the area after the blast, indicating an internal clash.
Israel's Channel 10 TV quoted Israeli military officials as saying Palestinian militants fired an anti-tank rocket at the car.
Gaza has been hit by factional fighting between Hamas and its main rival, Fatah .
In June, Hamas militias overran the seaside territory, vanquishing the Fatah -linked security forces.