Local civil rights monitors put the death toll at 28, with some 100 people wounded in Rafah, on the Egyptian border.

In the worst inter-Palestinian violence in two years, six Hamas policemen and six civilians were among the dead. It exposed bitter tensions in the blockaded coastal strip, where Hamas has imposed its own nationalist brand of Islam while also trying to reach out to the West to end its international isolation.

Three children died, said Hamas officials who blamed the Jund Ansar Allah, or Warriors of God, and its al Qaeda-inspired leader Abdel-Latif Moussa for provoking the attack by declaring an “emirate”, or strict Islamic rule, in a sermon on Friday.

Foreign operatives

The death of a Syrian fighter also challenged denials by Hamas leaders that foreign al-Qaeda operatives were in Gaza.

Moussa, a middle-aged physician and local cleric, and an aide named Khaled Banat, a Syrian national of Palestinian origin, blew themselves up after killing a negotiator, the officials said.

Residents in the town of Rafah, still sealed off to the media by the Hamas forces, described a night of terrifying violence.

Hamas has ruled Gaza since routing the forces of Western-backed President Mahmoud Abbas in 2007.

The bloodiest internal fighting since then has exposed challenges to Hamas on its radical, pan-Arab Islamist flank as the nationalist movement strives for international acceptance and an easing of an Israeli embargo that has prevented reconstruction since Israel’s offensive in Gaza in January.