Speaking in Cairo on Saturday after talks with Hosni Mubarak, the Egyptian President, Mahmoud Abbas accused Hamas of reneging on a number of agreements with Fatah.
He said: "Unfortunately after this agreement was signed there were regressions from it ... and unfortunately we are back to point zero, and we will examine the issue anew."
On Friday, the Hamas Palestinian prime minister, Ismael Haniya, said he could not lead a government that recognised Israel.
Meanwhile, on the ground, Israeli tanks entered the northern Gaza Strip in a raid the army said was to stop Palestinian fighters firing rockets.
Palestinian witnesses said the tanks moved on to farmland near the town of Beit Hanun on Saturday.
Internal Palestinian clashes also erupted in the northern Gaza town of Beit Lahiya, witnesses said.
They said shots were fired when members of a Hamas-led security force stopped fighters from the al-Aqsa Martyrs Brigade, which is loyal to Abbas, from entering a hospital with their weapons.
One security force member was wounded, the witnesses said.
Later, some 3,000 government employees and supporters of Abbas and his Fatah movement rallied in Gaza City and called on him to sack Haniya's government for its inability to pay their salaries.
A Western aid embargo has prevented the Palestinian goverment from paying salaries to its 165,000 workers since March.
Israel has also banned Palestinians from travelling there during the Jewish new year festival of Rosh Hashanah.
The Israeli military said in a statement it would make exceptions for teachers, medical workers and some of those participating in religous ceremonies.
Around 3000 Palestinian farm workers would also be allowed into Israel to harvest olives, the statement said.
The ban will last until Sunday, the military said.