Investigators scour the bomb site
A bomb has exploded outside the Athens stock exchange, slightly injuring a female passer-by and damaging the building, police say.
The bomb - which set fire to several cars - was hidden in a stolen van.
Another bomb went off outside a government building in Thessaloniki, causing minor damage and no injuries.
The blasts may be the work of a Greek extremists' group, Revolutionary Struggle, says the BBC's Malcolm Brabant in Athens.
Earlier this year the group claimed responsibility for two bombs aimed at the American Citibank group.
A warning of the Athens explosion was telephoned to a local newspaper, enabling police to seal off the area in the west of Athens before the bomb went off.
Several cars were set on fire by the explosion
The windows at the bourse were blown out, and a neighbouring car dealership was damaged along with nearby trees and parked cars.
One passing woman was slightly injured by flying glass, but there were no injuries inside the building and the stock exchange opened as normal.
"We know for the moment that there is damage to a number of staff workstations and desks, but the core operations are up and running," a bourse spokesman told AFP.
The bomb in Thessaloniki caused minor damage around the ministry responsible for Greece's two northern provinces of Macedonia and Thrace.
In a letter to a satirical newspaper, Revolutionary Struggle had promised more attacks against economic targets.
It said: "We need to rid ourselves for good of all the scum of economic and political power so that humanity can free itself from these criminals."
Greece has been dogged by unrest since police shot a teenager dead last December.
The death sparked the country's worst riots in decades, leading to clashes between police and protesters in the weeks that followed.