Spanish Prime Minister Jose Luis Rodriguez Zapatero welcomed the move but emphasized that rebuilding the peace process would take time.
"The position of the government is one of caution and prudence. After so many years of horror and terror, it will be a long and difficult process," Zapatero said in an address to the parliament.
Three members of ETA, dressed in black suits with white hoods and black berets, announced the cease-fire on Spanish state television. A woman seated in the center of the group said, "ETA has decided to declare a permanent cease-fire from March 24, 2006. ... The aim of [the cease-fire] is to promote a democratic process in the Basque country and to build a new framework in which our rights as a people will be recognized."
She called on the Spanish and French governments to "respond positively" to the cease-fire.
ETA, which stands for Euskadi ta Askatasuna or "Basque Fatherland and Liberty", is the most active group fighting for independence for the culturally and linguistically independent Basque region that is part of northern Spain and southwest France.
Bombings in the past have targeted members of parliament, judges, journalists, police officers, philosophers and intellectuals, business leaders and Spanish Prime Minister Luis Carrero Blanco in 1973.
ETA, labeled a terrorist organization by the United Nations and the United States, broke two cease-fires in the 1990s but many believe this latest effort may be different, coming nearly two years after al-Qaida terrorists killed 180 in a commuter train bombing.
The bombing contributed to the Socialist Party takeover of the parliament and hardened the sympathies of the Spanish public toward the Basque separatists, who had not carried out a lethal attack since a car bomb in 2003 took the lives of two police officers.
ETA attacks since May 2003 have been infrequent, mostly confined to small non-lethal bombings used to extort Spanish-owned businesses.