Aides to Mr. Abbas, who were not authorized to speak publicly, said one central reason the two sides were reconciling after four years of enmity was that Hamas had suddenly found itself in a position of weakness. Hamas is based in Syria, which is in turmoil, and it may not be able to stay there over the long term. Moreover, the aides said, Egypt may be friendlier to Hamas than it was under President Hosni Mubarak, but it is not heading down an Islamist path, as Hamas had hoped.

“They are in trouble, and so they reached out,” one Abbas aide said of Hamas.

Hamas figures presented a different picture of what led to the accord. They focused on Mr. Abbas’s frustrations with Israel and the United States in failed peace efforts and said that Fatah was therefore heading more in the direction of Hamas.

“There are no negotiations now, so let’s not speak about illusions that may or may not happen,” Taher al-Nounou, a Hamas spokesman, said when told of Mr. Abbas’s comments. “The Israeli government has nothing to offer to the Palestinians. It even refused to freeze settlements.” But he said that Hamas would abide by any P.L.O. negotiations and that it expected the P.L.O. to be reconfigured after elections in a year.

Mahmoud Zahar, a Hamas leader who was in Cairo for the Egyptian-brokered Palestinian negotiations, said he saw no place for peace talks with Israel under the new arrangement.