Greek authorities have seized a Tanzanian-flagged ship heading for Libya and carrying materials used to make explosives, the coastguard said on Wednesday.
The vessel was detected sailing near the Greek island of Crete on Saturday. Authorities found 29 containers carrying materials including ammonium nitrate, non-electric detonators and 11 empty liquefied petroleum gas tanks.
A large explosive device was found outside an apartment block in Metamorphosi, northern Athens, on Friday before it went off.
Explosives had been placed in a 30-liter container, which also contained three detonators, according to police who are examining the bomb for clues.
Officers did not provide further details about the potential victim or motives for the attack.