Mahmoud al-Zahar, a Hamas official in Gaza told Ma'an news agency the meeting was set for Thursday to bring an end to the ongoing dispute.
Fatah Central Committee member Azzam al-Ahmad said Wednesday he doubted a unity deal would be achieved, Ma'an reported.
Palestinian officials said al-Ahmad will be accompanied by Sakher Bseiso and Nasser Yousef.
Al-Ahmad said he had already attended several meetings in Lebanon with Hamas representative Osama Hamdan in recent months.
"We will see what they have to offer," the agency quoted him saying Wednesday.
Earlier this week, the London daily al-Hayat said forging Palestinian unity is crucial to any prospect for a Palestinian state based on peace with Israel. Hamas has so far rejected a pact proposed by Egypt to end its row with Palestinian Authority President Mahmoud Abbas's Fatah party.
The newspaper said to help reconcile the two factions, Egyptian intelligence chief Gen. Omar Suleiman met Masha'al in Saudi Arabia earlier this month