(Reuters) – A 15-year-old boy was killed and his mother and sister injured late Sunday after a bomb exploded outside a building in central Athens, police said.

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Bomb attacks by militant leftist groups are frequent in Greece and usually target police, public buildings or businesses. Sunday’s explosion was the first in years to kill someone. Urban violence increased in the country after the police shooting of a teen-ager in December 2008.

“A bomb exploded, we have one dead, a man who was dismembered, and two injured, a woman and her daughter,” a police official said.

Police later said the dead person was a 15-year-old teen-ager and that the injured women, were his 44-year-old mother and 11-year-old sister.

“The woman, who was slightly injured, and the girl, whose injuries were more serious, have been taken to hospital,” said the police official who declined to be named.

Police said the victims were Afghan immigrants.

The bomb, which went off outside an association for business management, also damaged cars and adjacent buildings. Police cordoned off the area and anti-terrorism police were investigating the scene.

“There was no warning, there was nothing,” a second police official said.

Several suspected members of guerrilla groups have been arrested in recent months.

Self-proclaimed guerrilla group Fire Conspiracy Cells claimed responsibility on March 22 for three small-scale bomb attacks against police and a far-right group.

Urban violence last caused the loss of human life in June 2009, when Rebel Sect, another guerrilla group, claimed responsibility for the killing of an anti-terrorism policeman.

(Reporting by Harry Papachristou and Renee Maltezou; Editing by Ingrid Melander and Paul Casciato)