Peace talks with Israel have failed and the Palestinians must launch popular and diplomatic campaigns to achieve statehood, Marwan Barghouti said in an interview from his prison cell.

Still popular and articulate despite five years behind bars, the 50-year-old activist is seen by some as a Palestinian Nelson Mandela, the man who could galvanise a drifting and divided national movement if only he were set free by Israel.

With U.S. peace diplomacy at a standstill, Barghouti said, there is no justification for the split between the Fatah movement he belongs to and the Hamas Islamists who control Gaza.

"I do not see that there are fundamental political differences between Fatah and Hamas," said Barghouti, a leading figure in the two Intifadas, or uprisings against Israeli occupation, waged by the Palestinians since 1987.

Convicted of murder for his role in attacks on Israelis, Barghouti was jailed for life by Israel in 2004 during the second Intifada, which broke out in 2000.

From his prison cell he responded in writing to questions from Reuters delivered by his lawyers.

Before his arrest, Barghouti had been seen as a contender to succeed Yasser Arafat as Palestinian leader -- a position assumed by current Palestinian Authority President Mahmoud Abbas after Arafat's death in 2004.

Though behind bars, he is still popular and still seen as a possible successor to Abbas, who has no obvious heir.

"In the shadow of the failure of negotiations and the absence of an Israeli partner for peace, the necessary strategy is firstly ending the division and restoring national unity," Barghouti said.

"There is no excuse in the world that prevents national reconciliation, especially in light of the latest developments and the blocked horizon for negotiations," he said.

The divisions among Palestinians, which Barghouti described as "a crime against the nation", boiled over in 2007 when Hamas seized control of Gaza, splintering the national movement.

He urged Hamas to sign an Egyptian reconciliation blueprint so legislative and presidential elections can be held.

FUTURE LEADER?

Asked if he would run for president, Barghouti said: "When national reconciliation is accomplished and there is agreement on holding elections, I will take the appropriate decision."

He is serving five life terms, so any chance of becoming the next leader depends on being freed by Israel in a prisoner swap.

A major prisoner exchange may be imminent, if negotiations succeed for the release of Israeli soldier Gilad Shalit after three years of captivity in the hands of Hamas.

Hamas opposes any permanent peace with Israel, while Barghouti believes in negotiating a deal with the Jewish state that would establish Palestinian independence in the West Bank and Gaza Strip with East Jerusalem as a capital.

But peace talks are at a standstill. Abbas has refused to return to negotiations without a complete halt to the Israeli settlement building, which Palestinians say is destroying their chances of establishing a viable state.

"Betting on negotiations alone was never our choice. I have always called for a constructive mix of negotiation, resistance, political, diplomatic and popular action," Barghouti said.

He called for a "popular campaign" against settlement activity, what he described as the Judaization of occupied parts of Jerusalem, the blockade of Gaza, land appropriation and the construction of the "racist, separation wall".

Israel says its West Bank barrier, a combination of walls and fences that at points thrusts deep into the occupied territory, is designed to keep suicide bombers out of Israel. Palestinians see it as a land grab.

Fatah leaders at the movement's congress this summer suggested civil disobedience rather than organised violence.

Barghouti did not say what sort of action he had in mind. (Editing by Douglas Hamilton and Samia Nakhoul)