"The truce will continue but it requires Israel to stop aggression against Palestinians and to release all the Palestinian detainees," Sakhar Habash, a member of the Fatah central committee, said on Thursday.
Delegates from the 13 factions had debated on Wednesday whether to declare an open-ended period of "calm" or one of three months.
Nayif Hawatma of the Democratic Front for the Liberation of Palestine (DFLP) said the factions had agreed on "an open-ended calm".
"The behaviour of (Israeli Prime Minister Ariel) Sharon's government will determine if it is possible for this calmness to be long lasting or short," he said.
Ceasefire Egypt is hosting the conference in an attempt to boost Palestinian leader Mahmud Abbas' attempts to win a ceasefire announcement.
Abbas and Sharon declared a ceasefire at a 8 February summit meeting in Egypt.
Armed groups say Israel must
halt expansion of settlements
Abbas was in Cairo on Wednesday trying to persuade resistance fighters from Islamic Jihad and Hamas to formally join the truce.
Abbas is hoping a ceasefire declaration would push Israel to carry out its promises - including the handover of five West Bank towns - and move the two sides back to the negotiating table.
Israel on Wednesday returned to the Palestinians security control over Jericho, one of the five towns Sharon promised to hand over at the February summit.
DFLP's Habash said the factions also agreed on "rearranging the Palestinian house", saying they would appoint a committee to "reform the Palestinian Council to achieve unity".
For its part, the resistance group Hamas said on Thursday a Palestinian agreement on a truce with Israel would expire at the end of 2005 if Israel did not meet the resistance's demands, including prisoner releases.
"What was agreed upon today is calm until the end of this year as a maximum period of time in exchange for an Israeli commitment to withdrawal from cities and release prisoners"
top Hamas official
"What was agreed upon today is calm until the end of this year as a maximum period of time in exchange for an Israeli commitment to withdrawal from cities and release prisoners," top Hamas official Muhammad Nazzal said.
Senior Palestinian officials said resistance fighters would not
retaliate for Israeli attacks during the period of calm "to give
the international community a chance to press Israel to
implement its commitments".
Armed groups also say Israel must halt expansion of settlements and the construction of a separation barrier in
occupied Palestinian land.