Hundreds of thousands of Spaniards have rallied in Madrid to protest at planned peace talks between the government and Basque separatists ETA and demanded the guerrillas lay down their arms.

Draped in Spanish flags and carrying photos of their dead, families of ETA victims joined opposition politicians to attack Prime Minister Jose Luis Rodriguez Zapatero’s plan to end 38 years of guerrilla violence.

Survivors of Madrid’s 2004 commuter train bombings joined the anti-government protest and called on Zapatero to probe deeper into the attacks that killed 191 people.

“We want to know the truth!” they chanted in the heat of Madrid’s Plaza Colon, amidst shouts of “Zapatero resign”.

A two-year investigation into the bombings ruled out involvement of the armed Basque group but the opposition Popular Party (PP) and some victim groups say ETA may have played a part.

“The Government has the people’s support to defeat ETA but it has no support to negotiate for political gains, or allow killers to achieve political gains that have cost so many lives,” PP President Mariano Rajoy told reporters.

The Government declared plans to hold talks with ETA after it announced a permanent ceasefire in March.

ETA is blamed for more than 800 deaths in its fight for an independent homeland in northern Spain and south-west France.

It broke ceasefires twice in the 1990s and Spaniards from across the political spectrum want proof the group has abandoned violence before talks begin.

The Opposition says talks with armed guerrillas is giving in to “blackmail”.

Some ETA victims groups shunned Saturday’s protest and said the PP was playing politics by linking the Madrid train bombings to ETA when the attacks were carried out by Islamist radicals.

“There are a lot of victims who don’t want to enter this political game,” Roberto Manrique said, vice president of the Catalan Association of Victims of Terrorist Organisations.

Protest organisers said around one million attended what was the fourth demonstration against ETA in less than 18 months.

Police put the number closer to 200,000.