Top Eta bomb expert alleged to be among four people arrested in raid in France.
The Basque Nationalist Party, which rules the region in northern Spain, also faced criticism from the separatists for trying to “rupture” the nationalist movement.
Dozens of Eta activists, including 22 in Spain and 19 in France, have been arrested in police crackdowns in recent months.
Earlier this week, Alfredo Perez Rubalcaba, Spain’s interior minister, said that some of the arrests in France were of “enormous importance”.
He said that some of the suspects had played a role in a bomb attack at Madrid’s Barajas airport last December that killed two people.
“It’s hard to know how many political refugees there are. We estimate there are about 2,000, but there is no list,” he said.
Eta, whose name stands for Basque Homeland and Freedom, is blamed for the deaths of more than 800 people during four decades of armed struggle for an independent Basque country in northern Spain and southwestern France.