A bomb exploded outside a police detention centre in Athens on Saturday, though no one was injured, Greek radio reported.
It was the third bomb attack in two days in the Greek capital, which has been rocked in recent weeks by strikes and protests over austerity cuts aimed at controlling the debt crisis.
Earlier on Saturday a bomb exploded outside the residence of the president of the Greek-Pakistani Association. On Friday a bomb went off outside the offices of the far-right organisation Golden Dawn in central Athens.
Officials reported varying degrees of damage after the explosions but no injuries.
The third bomb was planted at a bus stop in front of the detention centre. Its explosion shattered a number windows in the immediate vicinity.
It was not yet clear who was behind Saturday's attacks. But police suspected that one of the country's many autonomous left-wing groups may be responsible for Friday's blast.