Hamas officials said Fatah had reneged on a pledge to release prisoners
The Palestinian militant group Hamas says it will boycott reconciliation talks with its Fatah rivals in Cairo.
Hamas accused the Palestinian Authority President Mahmoud Abbas of arresting hundreds of its members in the Fatah-controlled West Bank.
Egypt has been trying to broker talks between the two factions and has proposed they form a "national consensus government".
The factions have been deeply divided since Hamas seized Gaza last year.
The talks, due to have started on Sunday, would have been the first official meeting between the two main Palestinian factions since the Gaza takeover.
Hamas official Moussa Abu Marzouk said Fatah had gone back on a pledge to release Hamas prisoners, Associated Press news agency reported.
Mr Abbas's forces have embarked on a security drive recently, trying to extend their authority across the whole of the West Bank.
Mr Abbas has embarked on a security drive in the West Bank
Hamas says it wants what it calls political prisoners belonging to it released, but Fatah says any detainees are not political but have committed crimes.
The boycott of the talks - before they had even begun - highlights the huge differences between Fatah and Hamas, says the BBC's Aleem Maqbool in Ramallah.
A meeting would have been a massive first step by the two sides towards forming a joint government, reforming their security services and discussing a date for presidential and legislative elections, our correspondent says.
The division of the Palestinians has been hindering efforts at pursuing a peace process with Israel.
US Secretary of State Condoleezza Rice is in the region trying to push forward the process but conceded on Thursday that a Middle East peace deal will not be reached by the end of the year.
US President George W Bush said a year ago that he wanted a peace deal signed before he left office in January 2009.