The Hamas movement ruling the Gaza Strip said on Thursday it would bar members of the rival Fatah party from leaving the territory to attend their first congress in 20 years.
The Islamist group "has decided not to allow members of Fatah in the Gaza Strip to go to the West Bank to participate in their sixth congress," Mahmud Zahar, a senior leader of Hamas in Gaza, said in a statement.
The travel ban would be lifted if Fatah freed all Hamas prisoners in the occupied West Bank.
"If they want their members to go to the congress, they must free all our prisoners," Zahar said.
The ban affects the more than 400 Fatah members who currently live in Gaza and are eligible to attend the congress, according to officials in Gaza and the West Bank.
Fatah is due to hold a congress on August 4 in Bethlehem, its first such meeting in 20 years, with some 2,000 delegates expected to attend from around the world.
Fatah delegates living in Syria and Lebanon would be allowed to attend the gathering, an Israeli official said after talks in Jerusalem between Prime Minister Benjamin Netanyahu and US National Security Advisor James Jones.
Speaking on condition of anonymity, the official said the decision was taken "in the framework of measures being taken by the Israeli government to ease the living conditions for inhabitants of the West Bank."
Tensions between the two main Palestinian factions boiled over in June 2007 when Hamas seized control in Gaza after a week of deadly street clashes.