The Palestinian militant group Islamic Jihad has attended a meeting of the Palestine Liberation Organisation executive committee for the first time.
Hamas leader Zahar met Abbas for talks but declined his invitation
PLO chairman Mahmoud Abbas chaired the Gaza City meeting, with a Jihad representative there as an observer.
Correspondents say Jihad and its larger rival Hamas have recently softened their stance towards PLO-Israeli ties.
Hamas reportedly turned down its invitation to the meeting, saying further consultations were necessary.
"We have agreed to participate in the executive committee of the PLO but we need more internal discussions on the mechanism," said Hamas spokesman Sami Abu Zuhri.
The Hamas leader in Gaza, Mahmoud Zahar, met Mr Abbas for talks on Monday.
He said progress had been made on long-standing disagreements over the PLO charter and the size of Hamas representation at inter-Palestinian talks held in Cairo earlier this month.
Hamas and Islamic Jihad are both violently opposed to a Jewish state and want to establish an independent Palestine including what is now modern-day Israel.
The PLO charter calls for the creation of a Palestinian state only in the West Bank, Gaza and east Jerusalem, land conquered by Israel in the 1967 war.
The formal PLO membership is not expected to be taken up by Hamas and Islamic Jihad until after the election for the Palestinian parliament in July.