Eta called off its 15-month ceasefire in June
The armed group Eta says its campaign of violence will continue until it achieves its aim of self-determination for the Basque region of Spain.
The statement, said to be the group's first since it called off a truce in June, is an apparent response to a recent wave of arrests of Eta members.
The separatist group has said it was responsible for a number of small explosions in the last three months.
The Basque group is blamed for more than 800 deaths in the past 40 years.
In the statement, Eta vows to "strike at Spanish state structures on all fronts".
French police have recently arrested a number of suspects
The purpose of this action was to "achieve democratic conditions which would allow for the defence of all political projects", the statement says.
It also says the group was responsible for four attacks in northern Spain in recent months, one of them during the Tour de France cycling race.
Spanish and French authorities have recently arrested a number of suspected Eta members.
Eta suspended its violent campaign from February 2006 to June 2007.
In its Sunday statement, Eta said it was not responsible for the failure of peace talks with the Madrid government, accusing it of "seeking to deactivate the Basque independence movement".
ETA is considered a terrorist organisation by Spain, the European Union and the United States.