MADRID — Spanish authorities averted potential disaster Friday when they dismantled a bomb on the Madrid-Seville bullet train track, a discovery that sent shudders through a public still reeling from train bombings 22 days earlier that killed 191 people.
The incident paralyzed much of Spain's heavily used train system just as millions of Spaniards were heading into Holy Week holidays, which officially began Friday. From Madrid to the provinces, trains and passengers were stranded in stations while police searched for additional explosives.
The discovery of the bomb raised the specter of a sustained campaign by extremists that is deadlier than anything Spain has seen. In Istanbul, Turkey, for example, bombings at two synagogues on Nov. 15 that killed and wounded dozens of people were followed five days later by an even bloodier attack.
No other bombs were found in sweeps of the railways Friday. Spain said it would deploy its army, helicopters, sniffer dogs and police to guard the train network.
Interior Minister Angel Acebes disclosed the discovery of the bomb at a news conference in which he also announced the arrest in France of a senior leader of the Basque separatist organization ETA. Acebes did not say whether the arrest was linked to the bomb found.
On March 11, 10 bombs left in backpacks and rigged to cellphones ripped through four crowded commuter trains within minutes of one another during the morning rush hour. More than 1,800 people were wounded, and the ruling party fell in elections three days later, in part because of voter anger over the bombings and the government's handling of the investigation.
Members of the newly elected Socialist-dominated parliament were sworn in Friday in a ceremony overshadowed by the bomb discovery and the ensuing railway havoc.
Acebes had blamed last month's deadly bombings at three Madrid-area train stations on ETA, even as evidence pointed to Islamic extremists. On Friday, he did not offer any indication of who authorities believe might be responsible for the latest bomb.
But two law enforcement officials told The Times that investigators were focusing on the same network now blamed for the March massacre: a group of mostly Moroccan extremists with ties to Al Qaeda.
"It appears to be Islamic terrorism," one senior official said. "We are investigating in that direction."
Six alleged members of the Moroccan group, including its purported leader, Tunisian national Sarhane Abdelmajid Fakhet, remain at large. Spanish authorities issued international arrest warrants for the six this week and said they believed the suspects probably had fled. A total of 14 people, 10 of them Moroccan, are in custody and charged with participation in the planning, execution of the attacks or aiding the attackers.
The Spanish government was an enthusiastic supporter of the U.S.-led war in Iraq, despite widespread public opposition. Al Qaeda operatives have repeatedly threatened to punish U.S. allies.
The bomb found Friday underneath the bullet line 40 miles south of Madrid consisted of about 24 pounds of explosive, concealed in a plastic shopping bag with a 450-foot cable leading to a detonator, Acebes said. A railway worker spotted a suspicious package and called police, who alerted a bomb squad.
Acebes said the explosive appeared to be the same type as the one used in the March 11 attacks: a pinkish, putty-like substance very common in Spain. However, the device lacked an initiator, like a cellphone or other trigger, he said. Whoever planted the bomb was probably startled and left before finishing the job, investigators said.
Although Friday's bomb did not explode, the psychological effect was enormous because it revived fears that were only beginning to ease after last month's attacks. The use of public transportation had just returned to normal.
About 23 million Spaniards had been expected to head for hometowns and vacation spots for the Easter week holiday. Seville is a popular destination for Easter because of its colorful religious processions, and thousands of people would ordinarily be traveling along the high-speed line from Madrid to the Andalucian city.
Choosing a holiday season for attacks is a tactic often used by ETA. But senior investigators said initial evidence pointed to Islamic militants. The idea that Islamic cells in Spain -- despite the large number of arrests after March 11 -- would muster the wherewithal to attempt a follow-up strike has rattled Spanish security forces, a law enforcement official said.
Times staff writer Wilkinson reported from Rome and special correspondent Mateo-Yanguas from Madrid. Times staff writer Sebastian Rotella in Paris contributed to this report.