MADRID, Spain (CNN) -- At least 173 people were killed and nearly 600 injured in a series of explosions on Madrid's railway network at the height of morning rush hour, Spain's interior minister says.
The most deadly blast happened on a train entering Atocha station.
Spanish officials are blaming the Basque separatist group ETA for the coordinated attack, which comes ahead of Sunday's general election.
European Parliament President Pat Cox called the attack "the worst act of terror in the history of Spain and the worst act of terror in memory in any European Union state."
Spanish Interior Minister Angel Acebes said there were a total of 13 explosions at the Santa Eugenia, El Pozo and Atocha stations. He said there was "no doubt" ETA was responsible.
The most deadly blast happened on a train entering Madrid's main Atocha station, Acebes said.
Survivors described scenes of chaos and panic in the Spanish capital.
Survivors used mobile phones to tell relatives they were alive.
"The worst was people screaming for help inside the train and there was nothing we could do," one survivor told CNN+.
People in tears walked away from the city's main Atocha station in droves as rescue workers carried bodies away from the scene.
Many people with bloodied faces sat on curbs, using mobile phones to tell loved ones they were alive. (More eyewitness)
The attack comes ahead of Sunday's general election in which Spain's conservative ruling Popular Party -- which has taken a hard-line stance against ETA -- is currently leading in the polls.
So far, there has been no claim of responsibility.