A steamroller slowly drove over three rows of weapons laid out in the courtyard of a Guardia Civil police barracks south of Madrid, watched by representatives of terrorism victim associations and law enforcement agencies which fought against the group.

"We have just witnessed an act of great symbolism in that long fight against terrorism that was so painful for our country," the Socialist premier said.

"We will not be able to recover the lives that were lost, nor will we be able to erase the dark past as we have now destroyed these weapons, but we can fight against forgetfulness and repair the pain and honour" of the victims, he added.

Ninety percent of the nearly 1,400 weapons were seized from ETA between 1977 and 2005 and the remaining 10 percent belonged to GRAPO, an armed far-left group which is no longer active.

The weapons will now be melted down and transformed into a monument symbolising the end of ETA, which is accused of killing more than 850 people during its four-decade campaign for an independent Basque state in northern Spain and southern France.

"It is a symbolic day where we commemorate the victory of the rule of law over terrorism," Interior Minister Fernando Grande-Marlaska, a former judge from the Basque Country known for his role in the fight against ETA, told AFP at the event.

"To remember what happened is a mechanism to prevent it from being repeated in the future," he added.

Both ETA and GRAPO were classified as a terrorist group by Spain as well as the European Union.

"Behind these pistols, rifles and machine guns, there are many tragedies, many victims, which we must remember," said the head of the Memorial Centre for Victims of Terrorism in Spain's Basque Country, Florencio Dominguez Iribarren.

Some associations of victims boycotted the ceremony, as did the main opposition conservative Popular Party (PP), which called the event "propaganda".

They are angered by the support Sanchez's minority leftist coalition government receives from Basque separatist party Bildu, which includes former ETA members in its ranks.

They also oppose the transfer of jailed ETA members to prisons closer to the Basque Country, which they argue has increased under Sanchez's government.