During the fighting Hamas fighters overran several compounds used by Abbas's Fatah movement, while Fatah members also stormed and burnt Gaza's Islamic university.
Three members of the Palestinian intelligence service, including a deputy chief commander, were killed in fighting with Hamas fighters in the Jabaliya refugee camp, security and medical sources said.
Another four bodies were discovered on Friday and about 180 Palestinians have been wounded in violence during the last 24 hours, said one medical source.
Dozens of members of President Abbas' presidential guard were wounded when Hamas fighters and members of the controversial Hamas "executive force" controlled fired a mortar into their training camp in Gaza City.
"Between 40 and 50 new recruits of the presidential guard were wounded and there are perhaps some killed," one Fatah official said.
"It is pitiful to witness the bloody scenes in Gaza between the brothers"
Presidential guards stormed the Islamic University in Gaza City overnight, a known Hamas stronghold.
An explosion took place inside one of the campus buildings causing a large fire, witnesses said, at what is reputedly the most prestigious Islamic university in the impoverished Palestinian territory.
Ismail Radwan, a Hamas spokesman, said: "We heavily condemn this action of the presidential guard and its acts of vandalism committed at the Islamic University, which is an academic institution without armed men or stashes of weapons."
Several gunmen were detained, while weapons and explosives were confiscated during an initial sweep of the campus, a security source said.
Fatah said the operation had been ordered after Hamas fighters fired mortar shells and rocket-propelled grenades towards Gaza's main presidential compound from the university.
The four sponsors of the Middle East peace process – the EU, Russia, UN and US – are due to meet in Washington on Friday in a bid to fast-track peace efforts.
|The Islamic University in Gaza was |
stormed by Fatah fighters [AFP]
Condoleezza Rice, the US secretary of state, is likely to press for a renewed push to support Abbas in his power struggle with Hamas, which won a general election in January 2006.
Hamas has accused Washington of trying to provoke a Palestinian civil war by granting $86 million to bolster Fatah security forces.
Six Palestinians were killed and another 70 wounded on Thursday, after Hamas ambushed of a presidential guard supply convoy from Egypt.
One guard was left dead although Fatah denied the trucks were transporting weapons.
Weapons are being supplied by key US allies Jordan and Egypt, with US encouragement and Israeli approval.
Israel's deputy defence minister, Ephraim Sneh, said: "If Gaza will be under Hamas's control, it will very bad for Israel's security."
Sneh did not comment specifically on the new weapons being given to Abbas's forces.
Hamas has struggled to govern since taking office in March under the weight of US-backed sanctions imposed over its refusal to recognise Israel, renounce violence and accept existing interim peace deals with the Jewish state.
Diplomats say Abbas' military build-up was meant to counter moves by Hamas in smuggling more powerful weapons into Gaza.
Israel and other Western countries have accused Iran, under world scrutiny for its nuclear programme, of supporting Hamas financially.