A car bomb exploded at a trade fair center on Madrid's outskirts early Monday, but no one was reported injured, police said.
The bomb went off shortly after 9 a.m. (3 a.m. EST) at the Campo de La Naciones center about 90 minutes after the Spanish Red Cross received a warning call, a police spokesman said.
Nearby buildings were damaged but no one was hurt, the spokesman told The Associated Press on condition of anonymity, in keeping with police department rules. The area had been cordoned off after the bomb warning, he said.
It was not immediately known if any group claimed responsibility, but the armed Basque group ETA regularly sets off car bombs as part of its 40-year-long campaign for Basque independence.
Basque candidates banned
Monday's explosion occurred hours after the Supreme Court banned candidates from two Basque parties from taking part in upcoming regional elections because of alleged links between the two groups and ETA.
ETA, whose name is a Basque-language acronym for Basque Homeland and Freedom, has killed more than 825 people since 1968.
ETA called a cease-fire in March 2006, but resumed violence in December that year with a car bomb at Madrid's international airport that killed two people.
Recently the group claimed responsibility for the fatal shooting of a Basque businessman and a car bomb outside a Basque television station in December.