Two explosive devices targeted cars belonging to the Italian embassy in Greece on Friday, one of which went off causing no injuries, Greek police said.
There was no immediate claim of responsibility and officers said they were investigating.
A homemade bomb exploded at around 4:00 am (0200 GMT), damaging a vehicle parked at the home of an embassy officer in an Athens suburb, police said.
The other device, placed near a second diplomatic vehicle, did not go off.
Italian Prime Minister Giorgia Meloni expressed "deep concern" at what she called an "attack... probably of anarchist origin".
The far-right leader sent her "personal thoughts and those of the Italian government to the first counsellor of the Italian embassy in Athens, Susanna Schlein".
Meloni added she was following the case "with the utmost attention" and through Foreign Minister Antonio Tajani who was in Athens for talks on Friday.
The Greek foreign ministry "strongly condemned the attack" and said such "unacceptable" acts "would not disrupt... the excellent relations and ties of long-standing friendship between Greece and its partner and ally Italy".
Crude, homemade devices, which cause damage but rarely injuries, are commonly used against political or diplomatic targets, banks or foreign companies in Greece.
Police often blame groups on the extreme left or anarchists.