"We announce all of the military wings are united in their position and faith and that we consider any attack on any one of us as an attack on us all," eight factions, including Hamas, Islamic Jihad and the al-Aqsa Martyrs Brigades, said in a statement on Saturday reported by Reuters.
"Any action aimed at spreading chaos or internal strife ... will be considered treason," said the statement, issued at a Gaza news conference attended by armed men, some of them masked.
"Our response will be unified and swift."
In the latest in a series of kidnappings widely thought to stem from factional rivalries, a Hamas member was abducted by unidentified armed men in the West Bank on Friday but was released within hours.
The groups also stated that they have no intention of giving up their weapons or the struggle against Israeli occupation, AFP reported.
"Giving up the weapons would play into the hands of the enemy and any attempt to disarm us would meet strong resistance," the groups said.
Masked Palestinians stand guard
during the Gaza news conference
"Carrying on the struggle is a strategic choice and the Israeli withdrawal from the Gaza Strip does not mean that the Gaza Strip is excluded from the struggle."
The eight groups that issued the statement were the Al-Aqsa Martyrs Brigades, Al-Qassam Brigades, Al-Quds Battalions, Abu Ali Mustafa Brigades, National Resistance Brigades, Nasser Salah al-Din Brigades, Abu Al-Reesh Brigades and Martyr Khalid Abu Akir groups.
Abbas has called on resistance groups, which have spearheaded anti-Israeli violence over the past five years, to end what he describes as armed chaos and stop carrying their weapons in public.
Israel has complained he has not gone far enough and must disarm the factions in accordance with a US-backed "road map" that charts mutual steps leading to the creation of a Palestinian state.
Abbas, who declared a truce along with Israeli leader Ariel Sharon last February and coaxed factions into announcing a "period of calm" until the end of the year, wants to co-opt armed men rather than confront them, citing fears of civil war.
The two are expected to meet as early as Tuesday ahead of Abbas's White House talks with US President George Bush on 20 October amid heightened hopes for peacemaking after Israel's completion of a pullout from the Gaza Strip on 12 September.
Israeli and Palestinian officials plan to meet on Sunday for another round of preparatory talks ahead of the Abbas-Sharon summit, which is not expected to yield any breakthroughs.
Israel's Silvan Shalom demanded
a crackdown on the groups
Speaking on Israel Radio, Israeli Foreign Minister Silvan Shalom reaffirmed Sharon's refusal to restart talks on Palestinian statehood until Abbas cracked down on armed factions.
"Our demand is unequivocal: they have to act against terrorism decisively," Shalom said.
"I think if they do that, we would be willing to take a long series of measures that would ease things for them. Our aim is to march together towards a resumption of talks, but in accordance with the road map and devoid of shortcuts which the Palestinians are interested in."
Progress reported on border deal
Israel and the Palestinians are moving towards an internationally brokered agreement on new security arrangements for the Gaza Strip's border with Egypt, Israeli and Palestinian officials said on Saturday, The Associated Press reported.
A deal could allow Palestinian residents in the coastal strip relatively free movement but would have to address Israel's security concerns. Israel fears that fighters and weapons will reach Gaza more easily without Israeli inspectors.
Envoy James Wolfensohn (L)
briefed Abbas on Friday
Under a compromise proposal brokered by international mediator James Wolfensohn, Palestinian travellers and exports leaving Gaza would go through Rafah, with foreign inspectors supervising the traffic.
Incoming goods would be rerouted through Kerem Shalom, an Israeli-run inspection point on the meeting point of Gaza, Egypt and Israel.
Wolfensohn briefed Abbas on the negotiations on Friday and told him that Israel agreed in principle to the presence of European inspectors, said a Palestinian official who participated in the talks.
Wolfensohn told Abbas he hopes to wrap up a Rafah deal by the end of Ramadan in early November, the Palestinian official said. He spoke on condition of anonymity because he was not authorised to talk to the media.
A senior Israeli official said late on Saturday that Israel is open to the idea of foreign monitors on the border and that the Wolfensohn plan is one of the options under consideration.
Also on Saturday, the Palestinians broke ground on their first major development project in Gaza since the withdrawal, a $100 million complex that will provide housing to 25,000 people. The development, funded by the United Arab Emirates, is being built on the former Jewish settlement of Morag and is expected to take two years to complete.