MADRID, Spain (CNN) -- A car bomb exploded Wednesday morning in northeastern Madrid, lightly injuring three people, emergency workers say.

A spokeswoman for Spain's Interior Ministry said a warning call had been made to a Basque newspaper, Gara, ahead of the blast at 9:30 a.m. -- a tactic typically employed by the Basque separatist group ETA.

Gara's Web site said an anonymous phone call in the name of ETA was made to the newspaper at 8:45 a.m., saying a car bomb would explode 45 minutes later in a Renault Express -- a small truck -- parked at the corner of Rufino Gonzalez and Alcala.

A video camera positioned in the capital showed thick black smoke rising into the air.