The joint press conference has been spurred by common opposition against US President Trump's controversial peace plan, which paves the way for Israel to annex territory in the occupied West Bank.
Palestinian rivals Fatah and Hamas have pledged unity against Israel's occupied West Bank annexation plans in a rare joint conference on Thursday, as signs emerged of a rift between Israel and Washington over the project.
The relationship between Fatah, which controls the Ramallah-based Palestinian Authority, and Hamas — in control of the Gaza Strip — has been plagued by divisions for more than a decade.
The joint press conference was spurred by common opposition against US President Donald Trump's controversial peace plan, which paves the way for Israel to annex territory in the occupied West Bank, including Jewish settlements considered illegal under international law.
"We will put in place all necessary measures to ensure national unity" in efforts against annexation, senior Fatah official Jibril Rajub said in Ramallah at the press conference, also addressed by Hamas official Saleh al Arouri by video-link from Beirut.
"Today, we want to speak in a single voice," Rajub affirmed.
Arouri described the conference as "an opportunity to start a new phase that will be a strategic service to our people in the most dangerous stages."
But for former PA official and Palestinian analyst Ghassan Khatib, Thursday's show of unity was unlikely to spark wider cooperation between the two Palestinian groups.
"I doubt the annexation challenge will help these two factions to end their split and unify again. I don't think this is going to happen," Khatib told AFP.
"They'll appear together and they'll agree about the significance and the importance of the annexation and the need to try to coordinate their efforts but I don't think they'll go beyond that," he added.
Bibi, White House divide?
Prime Minister Benjamin Netanyahu's centre-right coalition government had set July 1 as the date it could begin implementing Trump's annexation proposals.
But the US plan, unveiled in January, also calls for any annexations to come as part of a larger peace package, including negotiations on the creation of a demilitarised Palestinian state across roughly 70 percent of the occupied West Bank, with a link to Gaza.
The US aside, the international community has voiced near unanimous opposition against unilateral moves by Israel. Netanyahu held off on making a potentially inflammatory annexation announcement on Wednesday.
Experts say there is evidence emerging that Netanyahu's desired roadmap for moving forward is at odds with Washington's.
Former US president Barack Obama's envoy to Israel, Daniel Shapiro, now a fellow at Tel Aviv's Institute for National Security Studies, told AFP the US wants action on the plan to be endorsed by Netanyahu's coalition partner, Defence Minister and alternate Prime Minister Benny Gantz.
'Annexation must wait'
Gantz, who is due to take over as prime minister in November 2021, has raised concerns about igniting regional tensions and said annexation must wait until the coronavirus pandemic has been contained.
The Trump plan also calls for talks with the Palestinians and buy-in from Gulf Arab states that would theoretically be tasked with providing massive funds for a nascent Palestinian state's economy.
"Those are all steps that are hard for Netanyahu to absorb, given what his base wants, which is a more expansive annexation, with less coordination with other players ... and without giving anything to the Palestinians," Shapiro said.
"So I think there is tension between Netanyahu and the White House on this right now."
Netanyahu, who has publicly voiced full-throated support for the Trump plan, said on Wednesday that talks with US officials were ongoing, although he has not laid out a timeline for specific action.