Police are believed to have found remnants of a pressure cooker in the wreckage created by the bomb that exploded at a shopping mall in Athens on Sunday morning.
The urban guerrilla group Conspiracy of the Cells of Fire has carried out attacks using pressure cookers to construct explosive devices in the past but authorities are not making any direct connections at this point.
No group has claimed the attack so far.
The bomb was left in a newspaper stand in the underground parking lot and an anonymous caller left a warning with Eleftherotypia newspaper and zougla.gr news website about 50 minutes before the explosion, which occurred at 10.40 a.m.
About 200 people were evacuated from The Mall in Maroussi. Two guards suffered injuries during the blast.
Police are also examining CCTV footage amid reports that there are images of two men leaving the explosive device.
The US State Department has warned American citizens in Greece to be on alert following the latest spate of apparently politically motivated attacks.
The Council of State, Greece’s highest administrative court, is expected to rule in the next few weeks on whether The Mall, whose retail space covers some 60,000 square meters, was built legally.