The two-day talks will focus on "the return (of the unity government) in the Gaza Strip and the implementation of its authority without obstacles," said the head of Fatah's delegation, Azzam Al-Ahmad.
The talks come after a joint Palestinian delegation and Israel agreed to hold indirect talks in late October to thrash out a lasting truce in Gaza.
Under Egyptian mediation, Israel and the Palestinians agreed on August 26 to a ceasefire that ended a 50-day war between Hamas and Israeli forces.
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But in order to negotiate with Israel in October, internal Palestinian divisions must be put aside and the two rival factions must agree on a unified strategy during talks with the Jewish negotiators.
The Palestinian rivals set up a unity government of independents in June but are at loggerheads again, with Abbas threatening to end the administration and accusing Hamas of running a "parallel government" as de facto ruler in the Gaza Strip.
Hamas in turn accuses Abbas's Palestinian Authority, headquartered in Ramallah, of not paying its 45,000 employees in Gaza.
The unity government is also crucial ahead of an international donor conference on October 12, to be hosted by Cairo, on the reconstruction of Gaza.