Spanish police said Thursday they had found a car packed with 200 pounds of explosives in Spain's northern Basque region.

The abandoned car was found near the northern town of Amorebieta and was rigged to be used in an attack, a police spokesman said.

The Basque interior department said the explosives were ready for "immediate" use and only lacked a detonator.

Police searching the area noticed the car had been parked for several days, and upon examining it found suspicious stains inside. They expanded their search and found the drum with the explosives, the department said.

News of the discovery came as Spain's prime minister toured the wreckage of Madrid's airport parking garage, hit by a bomb, and he warned the Basque separatist group ETA that neither the Spanish government nor its citizens will be intimidated.

"It will achieve nothing," Prime Minister Jose Luis Rodriguez Zapatero said after his tour of the shattered concrete structure. "It is not going to intimidate anyone."

ETA has not claimed responsibility, but the armed group is the only suspect in the bombing, which left one man dead, another missing and the nine-month-old peace process in ruins.

Zapatero said he is determined to end ETA's nearly four-decade campaign of violence, aimed at winning an independent Basque homeland, but he gave no indication of what his next move will be.

Click here to go to FOXNews.com's Europe Center.

Firefighters and police investigators escorted Zapatero during his tour of the flattened, five-story parking structure at Madrid international airport's new Terminal 4.

The blast killed an Ecuadorean immigrant, whose body was found in the rubble Wednesday. Rescuers are still looking for the missing man, also Ecuadorean, but do not expect to find him alive. Another 26 people were slightly injured. The death marked the first fatality in an attack blamed on ETA in more than three years.

ETA had declared a permanent cease-fire in March. The bombing prompted Zapatero's government to cancel plans for talks with the group.

ETA and its political supporters complained that the peace process was stalled because the government refused to make preliminary concessions. ETA has asked that its prisoners be moved from jails around Spain to the Basque region, and that the government halt police arrests and trials of ETA suspects and pro-independence politicians.

ETA has not claimed responsibility, but a man who called to warn authorities before the explosion said he represented the group.

The attack, which came one day after Zapatero said he was optimistic about the peace process, was a major political setback for the prime minister, who faces a general election in early 2008.

Zapatero made ETA's dissolution a centerpiece of his political agenda. When he announced in June he would negotiate with the group, he infuriated conservatives who opposed talks with what they consider an active terrorist organization.

Zapatero met Wednesday night with relatives of Carlos Alonso Palate, the 35-year-old immigrant killed in the blast.