The main Palestinian political group, Fatah, has halted its primary elections in Gaza after militants raided some polling stations and fired in the air.
West Bank voting showed strong support for the young guard
"The Fatah General Committee... decided to freeze the election," the group said in a statement after an urgent meeting.
It said Monday's results would be void and the primaries would be rescheduled.
Gunmen also set fire to ballot boxes, saying the candidate lists in the second stage of primaries for January's parliamentary poll were not complete.
The first stage took place in the West Bank on Friday with a strong showing for jailed Palestinian uprising leader Marwan Barghouti.
For the first time Fatah candidates are being elected by ballot. In the past they were appointed by party leaders.
Barghouti is serving several life sentences in an Israeli jail.
He was convicted in 2004 of involvement in a number of attacks on Israeli civilians.
Barghouti, 46, won 34,000 out of 40,000 votes - affirming his status as one of Fatah's most popular politicians, say correspondents.
Palestinian analysts say his victory is also a victory for the Fatah young guard, which has been pushing for a stronger say within the movement.
Israeli Foreign Minister Silvan Shalom said there was no chance of Barghouti getting an early release.
About 463,000 people have registered to vote in the selection process.
There are 463 candidates in the West Bank and 311 in Gaza vying for a place on the final list to be presented to the electorate on 25 January.