The two sides also promised to stop media attacks against each other.
The reconciliatory gestures come a few days before an international donor's conference is set to open in Egypt next Monday.
The Palestinians hope to raise almost US$ 3 billion to rebuild Gaza after last month’s Israeli offensive. But determining how to send aid to Gaza's people is tricky because much of the international community shuns Hamas, which is viewed as a terrorist organisation.
Fatah is led by Mahmoud Abbas (aka Abu Mazen), who is also head of the Palestine Liberation Organisation (PLO), the only internationally recognised Palestinian body.
The two groups approach Israel differently. Hamas wants to destroy Israel, by means that include suicide bombers; Fatah is seeking a “two states” solution for the two peoples.
The gap between Hamas and Fatah has widened in the last three years. In 2007 the militant Islamist group took over Gaza, leaving the West Bank in the hands of Fatah.
Hamas has even accused its rival of running a Gaza spy ring for Israel during the last offensive. Fatah has charged Hamas of persecuting Fatah activists in Gaza.
Hamas-Fatah talks are also urgent because presidential elections are looming.
A caretaker national unity government is likely to be on the table in Cairo. It would run things until presidential and parliamentary elections are held in the two Palestinian territories. In the meantime, international aid could pour in to rebuild Gaza.
Most Palestinians remain cautious, not fully trusting either side.
In the past both Hamas and Fatah have been involved in corruption.