Jailed Palestinian leader Marwan Barghouti has withdrawn from next month's Palestinian elections.
Israel said it would not free Mr Barghouti
The surprise move, announced by an aide, comes 10 days after he declared himself a candidate to succeed the late Yasser Arafat as Palestinian leader.
Mr Barghouti is serving five life terms imposed by an Israeli court in June for the killing of four Israelis and a Greek monk.
The Israelis had said they would not release him if he were elected.
Mr Barghouti's aides announced his move at a press conference in Ramallah.
Aide Ahmed Ghneim read out a letter from Mr Barghouti that said he was supporting the candidacy of Mahmoud
Abbas, the choice of the mainstream Fatah party.
But the letter was also critical of Fatah, some members of which had condemned Mr Barghouti for splitting the party in running against Mr Abbas.
Mr Barghouti, Fatah's charismatic 45-year-old West Bank general secretary, was captured in 2002.
His letter also spelled out his opposition to the disarming of any Palestinian groups or any deal with Israel that did not secure the release of all Palestinian prisoners.
Opinion polls had suggested a close race with Mr Abbas
The aide said Mr Barghouti's wife, Fadwa, would formally withdraw her husband's candidacy on Monday.
Recent opinion polls had suggested there would have been a close race between Mr Barghouti and Mr Abbas on 9 January.
After Arafat's death, Mr Barghouti had expressed backing for Mr Abbas, 69.
But his supporters pressured him to change his mind.
He and they were angry at what they believed was Fatah's failure to appreciate his show of support, analysts say.
In particular, Mr Abbas made no statement demanding Mr Barghouti's release from prison ahead of any return to negotiations with Israel.
However, the Fatah leadership maintained a hard line and threatened to expel Mr Barghouti if he did not withdraw his candidacy.
The BBC's Simon Wilson in Jerusalem says that with the popular Islamic militant group, Hamas, boycotting the poll, there are now no other serious challengers in sight for Mr Abbas.