A roadside bomb exploded outside a major security headquarters in Gaza City on Friday.
No one was injured in the blast, and there was no immediate claim of responsibility. But Hamas blamed Palestinian President Mahmoud Abbas' Fatah group, whose forces Hamas routed in June to wrest control of Gaza.
Security forces in Gaza described the explosion as the largest in a wave of recent Palestinian bombings against Hamas targets in Gaza.
Ihab al-Ghussain, a Hamas security spokesman, said the roadside bomb was placed on the western wall of the national security headquarters, damaging the wall and nearby houses.
"Evidence suggests that Fatah supporters were involved in all the previous explosions," he said. "We demand from the Fatah leadership ... a clear position on these attacks or they will be held directly responsible."
Fatah has denied responsibility for the Gaza bombings.