International negotiators including former Taoiseach Bertie Ahern have called on armed Basque group ETA to declare a definitive end to violence.

"We call upon ETA to make a public declaration of the definitive cessation of all armed action," Ahern said after a one-day conference, which did not include the Spanish government or the outlawed ETA.

If confirmed, and accepted by Spain, it would mark a historic end to more than four decades of bombing and shooting in ETA's battle for an independent Basque homeland in northern Spain and southwestern France.

ETA took a significant step by declaring a unilateral ceasefire in January this year but the Spanish government is demanding that the outlawed group make it definitive by surrendering its arms and disbanding.

"ETA has to announce that the current ceasefire has become definitive and irreversible," an official of the Basque nationlist party PNV told AFP on condition of anonymity.

"The final decision has been taken," said the official on the sidelines of a San Sebastian conference, which is expected to push ETA to bring a definitive end to the violence, blamed for 829 deaths.

"It must say so this week," the official said.

The conference "is the stage that takes a step to that final decision", said the PNV official, adding however that even if ETA agrees to lay down its weapons it will not disband.

Former UN secretary general Kofi Annan is a leading delegate at the one-day San Sebastian conference, which does not include the Spanish government or any ETA representative.

Others in the conference include Sinn Fein party president Gerry Adams, Mr Ahern and former Norwegian prime minister and WHO chief Gro Harlem Bruntland.

The timing of the conference is important, coming before November 20 elections widely expected to turf the ruling Socialists from power and install the conservative Popular Party.

"The important thing is that probably we are putting an end to this," said Ramon Jauregui, minister responsible for relations between parliament and Prime Minister Jose Luis Rodriguez Zapatero's office.

Jauregui told Onda Cero radio he believed it was "very probable" that ETA would use a call by the conference for a definitive end to violence as cover to make an announcement along those lines.

ETA, born during the dictatorship of general Francisco Franco, has been edging towards a definitive end for some time, hastened by Basque secessionists who urge that the cause be defended with ballots, not bombs and bullets.

Severely weakened by the Spanish and French security forces, which detained successive waves of its leadership, the armed group has launched no attack on Spanish soil since August 2009.

In September this year, ETA announced that most of its 700 imprisoned members had agreed to support a definitive end to violence.

Mr Adams, a key member of talks that ended the IRA, said the conference was a "very, very significant step".

"Hopefully, we will see a step change in the situation arising from today's initiative," Mr Adams told RTÉ’s Morning Ireland.

A key to developing an end to conflict is to find an alternative and develop dialogue, Adams said.

"It is my view that can happen in the Basque Country in the same way as it happened in our country," he added.

"Obviously the Spanish government has to embrace such an approach. It is a two-way street, the whole business of peace-making."