Arnaldo Otegi, the jailed top leader of the banned political wing of Basque separatist group ETA, was a key backer of the outfit's failed peace talks with Spain's central government.

"Do not let the olive branch fall," he said before 15,000 supporters of his Batasuna party at the Anoeta stadium in the Basque city of San Sebastian in January 2004, just 30 months before ETA declared a "permanent" ceasefire.

Otegi was a mediator in the talks with the government during the ceasefure even though Batasuna had been banned in 2003 for its links with ETA, which is blamed for 828 deaths in its 41-year campaign for Basque independence.

He appeared shaken after ETA put an end to the ceasefire by setting off a bomb at a car park at Madrid's airport, killing two men, on December 30, 2006 as he publicly distanced himself from the group's use of violence.

"No one can claim to build an independent state through an armed struggle, and if they do it would be a mistake," he said without explicitly condemning ETA violence.

ETA officially called off its ceasefire on June 5, 2007, citing a lack of concessions by Spain's central government in their tentative peace talks with the government. Two previous ETA ceasefires had collapsed within just a few months.

Prime Minister Jose Luis Rodriguez Zapatero's government has adopted a hard line against ETA since the end of its truce, detaining dozens of suspected members of the group and of Batasuna.

Otegi was arrested just three days later in the Basque region as he was about ti give a news conference after a Supreme Court ruling that confirmed a 15-month prison sentence against him for glorifying terrorism.

The sentence stemmed from comments he made praising veteran ETA leader Jose Miguel Benaran Ordenana at a memorial service in December 2003.

Otegi was released from jail in August 2008 after spending just over a year behind bars as part of his sentence but was arrested in October 2009 on charges of seeking to rebuild Batasuna under a different name.

Spain's High Court sentenced him on Tuesday to two years in jail after convicting him once again of glorifying terrorism for comments he made at a 2005 tribute in the Basque region to a jailed ETA member, Jose Maria Sagarduy.

In November 2005 he received a suspended one-year sentenced for slandering Spain's King Juan Carlos during a news conference two years earlier by saying the monarch was "chief of the Spanish army, that's to say, the person responsible for the torturers".

Otegi has been compared to Sinn Fein leader Gerry Adams, who has been the public face of Irish republicanism in Northern Ireland for more than two decades.

In 2005 Adams appealed to the IRA to use words, not guns, to achieve its goal of ending British rule in the province and months later the group ordered its guerrillas to lay down its arms.

In a similar way, Otegi's speech at the Anoeta stadium was seen as leading to ETA's ceasefire declaration.

But while a peace deal was finally achieved in Northern Ireland in 1988 after three decades of violence that cost 3,600 lives, ETA has carried out scores of bombings and shootings since it ended its latest ceasefire.