The explosive device that ripped through the food court at Escuela Militar (Military School) station was made with a fire extinguisher and a clock that were planted in a trash can, officials said yesterday.
"This is an act that has the hallmarks of a terrorist act. There is not doubt about that," said government spokesman Alvaro Elizalde, adding that the authorities would launch an "energetic response."
Nobody took immediate responsibility for the blast, which follows a string of unsolved small bombings in Chile that took place in uncrowded places.
"At the moment, seven people have been taken to (medical) centers," police spokesman Mario Rozas told reporters.
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The injured included four women and three men, including one from Argentina who had a stomach wound, the medical emergency service said.
One woman lost fingers in one hand, not limbs as initially reported, officials said.
"My legs buckled because it made a terrible noise," a witness told a local news channel.
Authorities suspect the bomb was planted by two young people who fled in a car, said Deputy Interior Minister Mahmud Aleuy.
"The government will not rest until these people are brought to justice. These people tried to kill innocent Chileans," said Interior Minister Rodrigo Penailillo.
Past attacks have been claimed by groups using names of old anarchist groups. Nobody has been convicted in connection with the attacks.
After a lull, similar bombings have reemerged in recent months.
The government stepped up security after an explosive device blew up in a subway train on July 14 and a special prosecutor was named to investigate the attacks.
Francisco Bravo, the special prosecutor, said yesterday's bomb was similar to the one used in the July attack.