Campaigning is getting under way in the Palestinian parliamentary election amid doubts about whether the poll will go ahead as planned on 25 January.
Palestinians are to have their first general election in a decade
Palestinian leader Mahmoud Abbas has said he will postpone the vote if Israel refuses to allow Palestinians in East Jerusalem to take part.
His ruling Fatah party started its campaign at Yasser Arafat's grave while election rival Hamas rallied in Gaza.
Hamas is making a strong challenge in the first general election in 10 years.
The election is seen as a major test for Fatah, which is regarded as corrupt and ineffective by large numbers of Palestinians, the BBC's Matthew Price reports from Jerusalem.
Fatah has governed the Palestinians since the first and only parliamentary elections in 1996. But now its power is being challenged by the Islamists and polls suggest Hamas could take up to a third of the vote.
If the prospect of a strong showing disturbs Fatah, it horrifies Israel and its allies, who regard Hamas as terrorists, our Jerusalem correspondent says.
Mr Abbas said all Palestinian factions agreed there could be no election if Israel carried out its threat to prevent Palestinians from voting in East Jerusalem.
However, Hamas has been making clear it wants the election to go ahead - and critics charge that Mr Abbas is simply trying to buy more time to see off the electoral threat.
Israel is opposed to allowing Hamas to run in the elections
"We have told them [Fatah] that postponing the election will lead to a vacuum and to a dark future," leading Hamas candidate Ismail Haniya told a rally in Gaza City.
One of the most prominent Palestinian politicians, independent MP Hanan Ashrawi, was stopped by Israeli police from campaigning in the East Jerusalem on Tuesday.
She told the BBC she had gone there to start her political campaign and was carrying election posters when the Israeli police arrived and told her it was illegal for her to campaign in the area.
She was allowed to leave but one of her assistants was detained.
A spokesman for the Jerusalem police force said Israeli law states no Palestinian political activity is allowed in East Jerusalem, occupied by Israel since 1967.
But it is still unclear as to whether Israel will go through with its threat to ban actual voting.
Fatah opened its election campaign at the late Palestinian leader's tomb in Ramallah in the West Bank.
With Mr Abbas on a tour of the Gulf states, Fatah campaign manager Nabil Shaath delivered the keynote speech to supporters and candidates.
"We will fight to finish the occupation and the wall [Israel's West Bank barrier] and the settlements and establish a Palestinian state in a peaceful resolution to the situation in our region," he said.
Fatah, he added, also had a "programme to stop the corruption and establish the new foundations for a Palestinian state".
Hamas launched its campaign in Gaza City outside the home of one of its dead leaders, Sheikh Ahmed Yassin, who was assassinated by Israel nearly two years ago.