Marwan Barghouti, the senior Fatah leader who could be set free in a prisoner swap with Israel, appears to be already testing the waters for a possible bid to succeed the Palestinian President, Mahmoud Abbas.

In an interview yesterday in al-Quds newspaper, the charismatic leader criticised his rival for relying on negotiations alone in dealing with the Jewish state and said he is considering standing as a candidate if an agreement is reached to hold presidential elections.

Barghouti, serving multiple life sentences for five counts of murder, is the most politically significant prisoner among 960 Palestinians Israel could free if a deal is struck with Hamas for the release of Sgt Gilad Schalit, captured three years ago in a cross-border raid. His popularity and willingness to trim between pacific and bellicose positions have led to him being dubbed the Palestinian Mandela. Hamas has been pressing hard for his release to demonstrate that it is concerned about the entire Palestinian nation, not only its own members.

"The [peace] negotiations have failed but we don't rule out negotiations or reject them on principle," Barghouti told al-Quds. But, he stressed, they must be combined with "active popular resistance". It was a call for a return to the popular demonstrations of the first intifada uprising, in which Barghouti played a pivotal role until being deported in 1989. But he added, in a hint of opposition to attacks directed at civilians inside Israel, that resistance needs to be in accordance with international law.

Fifty years old, the veteran Fatah member from near Ramallah has alternated between warlike and peaceful positions over the past two decades, playing an active role in two revolts against Israel but also espousing a two-state compromise solution with the Jewish state. Israel's cabinet is divided over whether he should be freed, with Foreign Minister, Avigdor Lieberman, terming him "not just a murderer but a leader of murderers" while his freedom is being urged by the Infrastructure minister, Binyamin Ben-Eliezer, who remembers the Hebrew-speaking Barghouti as a pragmatist and supporter of the 1993 Oslo agreement.

During the second intifada uprising that broke out in 2000, Barghouti led marches to Israeli checkpoints, causing clashes with soldiers. He also made stirring speeches condoning the use of force to end occupation. His militant credentials seemed fixed when he was tried and sentenced to five life terms by Israel in 2002 for being a militia leader linked to the killing of four Israelis and a Greek Orthodox monk. He denied involvement in violence

Analysts say freedom for Barghouti will bring the resignation of Abbas as president of the Palestinian National Authority closer. Amid frustration with the Obama administration and Israel for the latter's refusal to agree to a full settlement freeze, Mr Abbas is at a dead end. He has said he will stand down before the next elections.

"Marwan's release would make clear there is an alternative, so it would speed the departure of Abbas," says Hani Masri, head of the Bada'il think-tank in Ramallah. Barghouti told al-Quds he would consider running for president, but only if the elections were set in the framework of a "national reconciliation" agreement between Fatah and Hamas. He hoped balloting will held in June.

Mr Barghouti's allies depict him as a potential saviour for Fatah, the movement founded by Yasser Arafat that has suffered setback after setback since his death, including Hamas's 2006 electoral victory and its armed takeover of Gaza a year later.

"He can win elections and he can also achieve a reconciliation with Hamas," says Qadoura Fares, a close associate and former Palestinian Authority minister. To prove the latter point, Mr Fares recalls that, from his prison cell, Barghouti oversaw a 2006 document drawn up with jailed Hamas leaders endorsing the establishment of a Palestinian state in the West Bank and Gaza, the areas Israel captured in the 1967 Middle East war. It was viewed at the time as offering implicit recognition of Israel by the Islamic group.

Barghouti: Palestinian unifier?

* The hugely popular Marwan Barghouti is seen as the best hope of replacing Palestinian National Authority's lame-duck president Mahmoud Abbas, and of overcoming the vicious feud between Fatah and Hamas.

* Hamas put his name at the top of the list of prisoners it wants freed. But other voices doubt his ability to heal the divisions. And there is a background of bitterness: in 2002, top figures in Hamas condemned Barghouti as a traitor, implying that he was being manipulated by the US.