Madrid, Spain ? In the most devastating terrorist attack in Spanish history, 10 bombs that detonated minutes apart ripped through crowded commuter trains early Thursday at three Madrid stations, killing nearly 200 people, wounding 1,400 and sending this capital into convulsions of shock and horror three days before a national election.

Authorities immediately blamed the Basque separatist group ETA for the deadliest wave of terrorism seen in Europe in almost two decades. But the scale of carnage went far beyond anything the separatists had ever carried out and led to speculation that other groups might be responsible.

Interior Minister Angel Acebes initially said it was “absolutely clear” that ETA was responsible. Late Thursday, however, he went before reporters to say police had recovered a stolen van with seven bomb detonators and a tape recording of Koranic verses read in Arabic. The van was found in a suburb where the targeted trains originated, he said.

“I have instructed security forces not to discard any line of investigation,” Acebes said.

A short time later, an Arabic-language newspaper in London said it had received a letter purporting to claim responsibility for the bombings in the name of al-Qaida, having “infiltrated the heart of Europe.”

The rush-hour blasts paralyzed Madrid. Political parties canceled what remained of their election campaigns, the right-wing government of Prime Minster Jose Maria Aznar declared three days of mourning, and frantic relatives searched for loved ones at morgues and hospitals.

“This is mass murder,” an ashen Aznar said after an emergency Cabinet meeting. “The date of March 11 now holds its place in infamy.”

A hellish scene of destruction and anguish repeated itself at the three stations, including Atocha, the largest in Madrid and a hub for subways and long-distance trains just south of the famed Prado Museum.

The Interior Ministry said the explosives and detonation devices in all 10 bombs — crammed into backpacks and bags left on the targeted trains or on station platforms — resembled those used by ETA in previous attacks.

At Atocha, the dead and dying lay alongside the tracks or in a makeshift triage center.

“There was blood everywhere,” said Angel Grandes, 39, who was waiting for the train at Atocha. “There was a 20-year-old boy, who came out all torn up. He came near me, I grabbed his arm and he fell. He died right there, at my feet.”

Two people injured by an explosion in a train wait for aid in Madrid, Spain. By nightfall, authorities had counted 192 dead, and many of the injured were in critical condition. Several children and pregnant women were among those killed, Spanish television reported.