A bomb exploded outside a Bank of Greece building in central Athens before dawn Thursday, causing some damage but no reports of injuries.
The explosion was heard throughout the area. It was preceded by two anonymous calls to a news website and a newspaper warning that a bomb had been planted in a car outside the central bank offices.
Police cordoned off the area, but did not immediately approach the actual site of the explosion.
As dawn broke, television footage from the area showed the remnants of a car in the middle of an Athens street, with debris strewn around. It was unclear whether nearby buildings were damaged.
The news site that received one of the anonymous calls said the caller warned a bomb containing 75 kilograms (150 pounds) of explosives had been planted in a car and would explode in 45 minutes' time.
The explosion comes hours before Greece plans to return to bond markets for the first time since its international bailout began four years ago.