Greek police say a bomb has exploded near the Acropolis in central Athens, but it was not immediately clear whether anybody has been hurt.
The bomb exploded on Wednesday, apparently targeting the house of a Greek shipowner, a police source told AFP news agency.
"An anonymous caller contacted a Greek daily and said the bomb would explode at 20:30 local time (18:30 GMT) outside the home of shipowner Tsakos," the police source told AFP.
"The police evacuated the area and so far there are no reports of injuries," the source added.
The bomb had been left in a black backpack outside the entrance of the building, the police source said.
The location of the attack is near the Odeon of Herod Atticus and a few hundred metres beneath the Acropolis, an area very popular with tourists.
The Tsakos group is one of Greece's main shipowning companies. It was not immediately clear which member of the family had been targeted.