A top official from Spain's governing party has begun talks with the banned Basque separatist group Batasuna.
Spain's opposition Popular Party has condemned the talks
The meeting between the Basque branch of the Socialist Party and Batasuna took place in San Sebastian.
Last week, PM Jose Luis Rodriguez Zapatero said he would start talks with Batasuna's military wing, Eta.
Eta declared a permanent ceasefire on 22 March. The group has been waging an armed campaign for more than 30 years and is blamed for more than 800 deaths.
The opposition Popular Party has said the talks with Batasuna amount to a surrender to terrorists.
Demonstrators chanted outside the hotel in San Sebastian where Paxti Lopez, who heads the Socialists' Basque branch, was meeting Batasuna leader Arnaldo Otegi.
The talks were likely to focus on lifting the ban imposed on Batasuna in 2003, correspondents say.
Last week, Mr Zapatero made a statement in parliament, promising to open talks with Eta, which is pressing for Basque independence.
Eta is deemed to have stuck to its ceasefire
But he said that "democracy will not pay any political price to achieve peace" with Eta and he did not give a date for the start of talks.
"The process is going to be long, tough and difficult. We'll handle it with determination and prudence, with unity and loyalty and always with respect to the memory of the victims," he said.
He said recognition of the different political viewpoints in the Basque region would set the ground rules for this process of dialogue.
Surveys show that the majority of Spaniards support his attempt to bring peace to the Basque region, but a large minority are completely against talking to Eta, correspondent say.
Many victims' associations accuse the prime minister of surrendering to terrorism.
They say the only way to defeat Eta is through the justice system and police actions.