French police say they have arrested two of the most senior figures in the outlawed Basque separatist group, Eta.
Arms and ammunition were found during the raids
Mikel Albizu, known as Antza, and his partner, Maria Soledad Iparraguirre, were among at least 18 people detained in a swoop in south-western France.
Officials said the operation was possibly the most significant blow against Eta in years.
The Spanish authorities say the arrests have probably saved dozens if not hundreds of lives.
The BBC's Katya Adler in Madrid says Mr Albizu is thought to be one of the most senior political figures in Eta.
His partner, Maria Soledad Iparraguirre, is one of the group's leading female figures.
The couple, both aged 43, had been on the run from Spanish justice for more than 10 years.
They were seized near the town of Pau, according to the Associated Press.
Their arrests were part of a series made in border villages along the French border where Eta militants have long sought refuge.
The suspects were captured in towns including Saint Pierre d'Irubek, Briscous, Ayherre and Hendaye, Spain's interior ministry said in a statement.
Spanish Interior Minister Jose Antonio Alonso says the raid is hugely important and an example of outstanding collaboration between the two countries.
Improved French and Spanish ties since the 11 September attacks have led to several high-profile Eta arrests, our correspondent says.
Spanish authorities now describe Eta as considerably weakened but still dangerous.
The armed group has been fighting for more than 30 years for an independent Basque state.