For the second time in just more than two months, Spain (search) on Sunday averted a bombing by the Basque separatist group ETA after the Civil Guard stopped a small truck and found about 1,100 pounds of bomb-making chemicals, officials said.
Two alleged ETA members were arrested, but their identities were withheld.
The plan was to "generate a massacre in coming days, if possible, in the center of Madrid," Justice Minister Jose Maria Michavila said.
Interior Minister Angel Acebes said the explosion was planned for "today, tomorrow or the day after," and had the power to blast a deep 40-yard-wide crater.
The Civil Guard stopped the truck at a checkpoint near the town of Canaveras, near Cuenca about 90 miles southeast of the capital Madrid. Authorities found a half a ton of potassium chloride compound, 65 pounds of dynamite (search) and 100 yards of core fuse and an electrical detonator.
Officials evacuated the town for five hours while they deactivated the explosives. Residents returned to their homes about five hours later, shortly before noon.
Police also raided homes in Basque Country (search), apparently searching for weapons or explosives.
On Dec. 24, police arrested two suspected ETA members and seized a 55 pound bomb on a train headed to Madrid's bustling Chamartin Station. A second device of about the same size was discovered before it could be put on the train, Acebes told reporters at the time.
The attempted attack comes two weeks before Spain holds national elections March 14.
The conservative ruling Popular Party used the potential disaster to criticize its Socialist challenger as being soft on terrorism. The Socialists rule the key regional government Catalonia, where its coalition partner recently held secret talks with ETA.
ETA, which stands for Basque Homeland and Freedom, subsequently declared a unilateral cease-fire in Catalonia.
"You have to defeat terrorism," not negotiate with terrorists, Javier Arenas, the Popular Party's third-ranking official, said. ETA is "weaker than ever, but it's going to keep trying to fill Spanish society with blood."
ETA has killed more than 800 people since 1968 in its armed campaign for independence of the northern Basque region. The group is classified as a terrorist organization by Spain, the European Union and the United States.