Clashes broke out in Gaza City early on Sunday, witnesses said, as Hamas-run security forces pressed a territory-wide crackdown on rival Palestinian factions after a deadly bombing.

The fighting erupted overnight when Hamas-run police moved to arrest members of the Army of Islam, a small, shadowy militant group believed to be linked to Al-Qaeda.

Witnesses said they heard heavy exchanges of gunfire and explosions in which several people were wounded, including militants and police, but medical officials were not immediately able to confirm the reports.

The clashes came as Hamas cracked down on rival movements suspected of planting a bomb on Friday night that killed five senior militants and a five-year-old girl, the deadliest Palestinian attack on the group since it seized power in the Gaza Strip in June 2007.

Hamas on Saturday blamed the attack near Gaza City on Palestinian president Mahmud Abbas's Fatah party, which it accused of trying to undermine its rule.

Since the explosion Hamas-run forces have arrested more than 200 people, security officials said, most of them members of Fatah, which was largely expelled from the Strip when Hamas took over.

Security forces have also raided some 40 offices, sporting clubs and charities, most of them linked to Fatah, confiscating computers and documents, according to the independent Palestinian Centre for Human Rights.

Fatah has denied any involvement in the blast and said the attack was part of an internal Hamas conflict.

The two main Palestinian factions have been bitterly divided since Hamas took over the Gaza Strip but the factional clashes that rocked the impoverished territory before the Hamas takeover had mostly ceased under its rule.