The arrests were ordered by Spain's leading anti-terrorism judge, Baltasar Garzon, who led moves to outlaw Batasuna five years ago when he accused it of being a front for the armed separatist group Eta.

The raid is the most dramatic crackdown on the Basque separatists since the socialist government of prime minister Jose Luis Rodriguez Zapatero was elected in 2004.

Calls for independence are becoming more strident in both the Basque country and in Catalonia ahead of Spain's next general election in March of next year.

The Batasuna leaders, including their spokesman Joseba Permach, were led away in handcuffs by plainclothed officers whose faces were hidden by hooded tops and balaclavas.

The raid coincided with more than 15 house-to-house searches throughout the region.

It is unclear what charges were being brought against the detainees, 16 of whom were said to be members of Batasuna's national committee.

Garzon is known to be investigating allegations that Batasuna financed the activities of Eta, which called off a 15-month ceasefire earlier this year.

The raid in Segura is the latest operation in a four-month crackdown against the separatists which included the arrest in June of Batasuna's leader Arnaldo Otegi on charges of "glorifying terrorism".

The only senior Batasuna activist still at liberty said the arrests were an attempt by the government to bolster its standing ahead of the elections.

Pernando Barrena, who missed the Segura meeting because he was in Pamplona, claimed Zapatero was pursuing "revenge" against Batasuna because the group had taken a "firm line" in peace talks last year.

"It was an operation of punishment against those who tried to negotiate, " he added.

Before Batasuna was banned in 2003, it represented about 15% of the Basque people on local councils and in the regional government.