French police on Sunday arrested ETA's military leader Oroitz Gurruchaga Gogorza and his deputy in a joint operation on the Basque separatist group with the Spanish police, Spanish and French authorities said.
Gurruchaga and "his deputy" Xabier Aramburu were arrested in the southwestern French village of Cauna while travelling in a stolen vehicle with fake numberplates, the Spanish interior ministry said, adding that both men were armed with a pistol and a revolver.
"The presence of both men in southern France could indicate they were setting up meetings to recruit new ETA members," the ministry said.
A French official confirmed that "two senior ETA members were arrested in the south."
Gurruchaga, 30, joined ETA in 2008 and rose through the organisation's ranks to become its military and recruiting chief, according to the ministry.
Spanish police believe Aramburu, 32, is responsible for a series of bomb attacks in Basque country in 2008, including the car bombing of a police station.
ETA is blamed for 829 killings during a four-decade armed campaign for an independent Basque homeland in northern Spain and southern France.
Sunday's arrests come just over a year after those of then-ETA military boss Alejandro Zorbaran Arriola, known as "Xarla", and three other suspected ETA militants at a rural house in northern France.
They bring to 15 the number of people arrested on suspicion of ETA ties since the group announced "the definitive cease of its armed activity" in October last year.
Despite the announcement, ETA has not surrendered any weapons or disbanded.
French Interior Minister Manuel Valls, who is due to visit Spain on Tuesday, joined his Spanish counterpart Jorge Fernandez Diaz earlier this month in calling for ETA to disband.
ETA is pressing for direct talks with the French and Spanish governments, but both ministers have rejected any negotiations.