|ETA is blamed for the deaths of 829 people in its four-decade campaign for a Basque homeland [EPA]
French police have arrested Alejandro Zobaran Arriola, the suspected military chief of the armed Basque separatist group ETA, Spanish national radio reported.
Arriola was among four ETA suspects held in an operation on Thursday by French police near the Belgian border, according to the radio report.
French sources close to the operation earlier confirmed that four suspected ETA members were arrested in the Pas-de-Calais region.
"Their identity and their importance" in the organisation "cannot be confirmed," they said.
Spain's leading daily El Pais said on its website the arrests took place in Willencourt, west of the city of Arras. The paper had earlier reported the location as Beaulencourt.
The arrests took place in a house where firearms and documents were seized, the sources said, adding that the operation was continuing during the night of Thursday to Friday.
Campaign of terror
ETA is blamed for the deaths of 829 people in its four-decade campaign of bombings and shootings to force the creation of a Basque homeland in northern Spain and southwestern France.
Spanish authorities believe their campaign against ETA has crippled its operational capacity, with dozens of arrests, including a number of top leaders, made in co-operation with forces in other countries, particularly France.
ETA declared on January 10 a "permanent and general ceasefire" to be verified by the international community.
It was the first unilateral declaration of a permanent ceasefire in ETA's campaign of bombings and shootings for a homeland independent of Spain.
But Spain's Prime Minister Jose Luis Rodriguez Zapatero rejected the declaration, saying he wanted nothing less than ETA's dissolution, and the authorities have vowed to hunt down ETA members.
ETA had announced a ceasefire in March 2006 within the framework of negotiations with Madrid. But nine months later, it set off a bomb in the car park of Madrid's airport, killing two men.
There has been no attack on Spanish soil since August 2009.