A makeshift bomb exploded outside a police detention centre in Athens on Saturday, causing minor damage but no injuries, Greek police said.
Police stopped traffic before the device went off in the third such bombing since Friday.
"There was a warning call to a newspaper about 15 minutes before the device went off. The blast damaged the guard post at the front of the building. There is no claim of responsibility," a police official said.
On Friday a makeshift bomb damaged the office of a far-right group in central Athens without hurting anyone. Early on Saturday another exploded outside the home of the head of the Pakistani community in Athens, causing only material damage.
Police suspect the two last blasts may be related to Friday's attack on the office of ultra nationalist group, Golden Dawn.
There has been a series of gas canister and bomb attacks by leftist and anarchist groups in Greece since the fatal police shooting of a teenager sparked the country's worst riots in decades in December 2008.