Pernando Barrena is the only top Batasuna leader still free
A senior leader of Basque separatist group Batasuna has called the arrest of 23 key members a "declaration of war" by the Spanish government.
Pernando Barrena is the only top leader still at liberty following a police raid on a party meeting on Thursday.
Batasuna was banned in 2003 for failing to condemn violence and cut links to Eta, which has killed more than 800 people in a four-decade campaign.
Eta called off a 15-month ceasefire earlier this year.
The separatists want an independent Basque state in northern Spain and south-western France.
Mr Barrena told journalists at a press conference in the northern Basque city of San Sebastian that Thursday's arrests were "kidnappings".
"This police operation uncovers the decision of the Spanish government, which is to issue a total declaration of war against Basque independence," Mr Barrena said.
The Segura raid was on a secret executive committee meeting
"The repression will not make us back down," he said.
Thursday's raid in the town of Segura was ordered by top anti-terrorism judge Baltasar Garzon.
He led the move four years ago to ban Batasuna.
Mr Barrena said the raid on the secret executive committee meeting was because of Batasuna's hardline approach to peace talks.
Judge Garzon is expected to question the detained members on Sunday.
On Friday, hundreds of people protested in Basque towns and cities against the arrests.
Thursday's operation was the latest in a four-month crackdown against Basque separatists that has included the arrest of Batasuna's leader, Arnaldo Otegi, on charges of "glorifying terrorism".
Before Batasuna was banned in 2003, it represented about 15% of the people in the Basque region on local councils and in the regional government.