Azzam al-Ahmed, a Fatah negotiator, traveled to Gaza on Monday for what he said would be a final round of talks with Hamas leaders about the Cabinet lineup, AP reported.
A temporary government of technocrats is to prepare for general elections in 2015.
"The declaration of the new government is Thursday," al-Ahmed told reporters.
He said Rami Hamdallah, the prime minister of the West Bank-based Palestinian Authority, would stay on to head the unity government. Acting Palestinian Authority Chief Mahmoud Abbas had previously agreed to take on the job of prime minister in addition to his position, but now seems reluctant to assume additional responsibility.
Ehab Ghussein, a Hamas government spokesman, said he expected the Cabinet lineup to be announced in the coming days, but did not give a date.
Negotiations about the Cabinet lineup began in April and were to be completed by late May.
Repeated reconciliation attempts have failed, but the rivals appear more flexible this time because both are struggling with crises.
The longstanding conflict between the rival factions peaked in 2007, when Hamas drove the Fatah movement of Abbas out of the Gaza Strip, leaving his forces confined to the Israeli-occupied West Bank.
Since then, both sides have run rival governments in their respective territories on opposite ends of Israel. Abbas seeks both the West Bank and Gaza as parts of a future Palestinian state, and the internal rift is a major impediment to any potential peace deal.
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