At least six people were wounded as clashes broke out in Gaza City on Sunday when Hamas-run security forces clashed with members of the Army of Islam group.
"Hamas forces came to arrest us early this morning, just after midnight," one member of the group, who asked not to be named, told reporters.
"There was fighting for several hours, with rocket-propelled grenades, explosions and gunfire, but they did not arrest anyone."
Friday's bombing on the beachfront in Gaza has raised the spectre of the factional violence, in which hundreds of people died, during which Hamas seized full control of the territory.
"We are afraid that the devil is pitting brothers against each other and they will shed one another's blood," Fatima Ahmed-Salama, a 40-year-old mother of six in Gaza, said.
Abu Adel, a 65-year-old man, said the internecine fighting harmed only Palestinians, not Israel. "I ask God to calm them down and make them stop before we have more dead," he said.
Hamas said that Fatah carried out the attack to undermine its rule, but Fatah has denied any involvement in the blast and said the attack was part of an internal conflict within Hamas.
Security forces have raided more than 120 offices, sporting clubs and charities, most of them linked to Fatah, since the bombing, confiscating computers and documents, according to the independent Al-Mizan Centre for Human Rights.
It also raided the houses of two Fatah leaders, Zakariya al-Agha and Ibrahim al-Naja, and confiscated their cars, a senior Fatah official told the AFP news agency on condition of anonymity.
Hamas officials have denied that the latest string of arrests was political.
"There were only a limited number of people arrested and most of them were later released," Sami Abu Zuhri, Hamas spokesman, said.
"We condemn this focus on the arrests, which are connected to the murder of five fighters and a child, while everyone ignores those who were arrested in the West Bank for political reasons."
Abbas has renewed calls for dialogue with Hamas, which won a majority in a 2006 parliamentary poll, and said an independent Palestinian committee should investigate Friday's blast.
Speaking after talks with Hosni Mubarak, the Egyptian president, Abbas said that the attack was regrettable and unacceptable, and that Egypt would invite representatives of Palestinian factions "within days" to dialogue sessions in Cairo.
Previous attempts to mend fences between the two sides have ended in failure.
Meanwhile, the Israeli army killed a senior Hamas fighter in the occupied West Bank on Sunday, according to Palestinian medical workers and Hamas officials.
|Shihab al-Natsheh's body was badly mangled when it was removed [AFP]
Israeli soldiers fired a shell at the house of Shihab al-Natsheh in the city of Hebron on Sunday after he refused to surrender and opened fire at soldiers, local residents said.
Other witnesses said Israeli soldiers surrounded the house, exchanging fire with al-Natsheh and eventually bulldozing the house hours later when he refused to surrender.
His badly mauled body was seen being removed from the rubble.
A Hamas statement said al-Natsheh, 25, was a member from the group, and said he fought the soldiers for 12 hours before he was killed.
The group's armed wing, the Izz el-Din Brigade, vowed to avenge Natsheh's killing.
"Our response will be swift and painful," it said in a statement.
The Israeli military confirmed it carried out the raid, saying that during the exchange of fire, troops heard explosions from inside the house, presumably from bombs stored inside.