Palestinian Authority President Mahmoud Abbas has called for Gaza's Hamas rulers to be "brought down", his strongest call yet for their removal.
Abbas's call comes after Fatah supporters were killed at a rally
Previously he has only demanded Hamas apologise for taking over Gaza and return it to Fatah security control.
His comments came after Hamas security forces killed eight Fatah supporters at a rally in Gaza on Monday.
A Hamas leader in Gaza, Ismail Haniyeh, has expressed regret for the deaths, and promised a public investigation.
He also said members of Hamas' security forces might have been at fault, and said he had ordered the release of people arrested if there was no evidence against them. But he added: "The guilty will be punished under the law."
Members of the Hamas-run Executive Force opened fire on the massive rally to commemorate the late Yasser Arafat, which turned into a protest again Hamas control.
Afterwards, Hamas moved to shore up its control of the narrow coastal strip.
It has rounded up more than 400 Fatah activists in Gaza during the week. It has also announced media restrictions and a plan to further curb public gatherings.
In his speech marking Palestine National Day, Mr Abbas said: "We have to bring down this bunch, which took over Gaza with armed force, and is abusing the sufferings and pains of our people."
Mr Abbas has set up an emergency government in the West Bank, while Israel - which considers Hamas a terrorist organisation - has tightened its blockade of the Gaza Strip.
Hamas won democratic elections for the Palestinian Authority parliament in 2006, but Mr Abbas has condemned the Gaza take-over in June as a putsch by Hamas.
In a separate incident, Israeli forces have killed two Palestinian militants and wounded three other people in northern Gaza.
Witnesses in Beit Lahyia said the Israeli fire followed rocket launches by Palestinian militants across the border into Israel.
The dead militants were identified as members of al-Aqsa Martyrs Brigade, an armed offshoot of Fatah.