Police were holding a Croatian man after two lighted petrol bombs were thrown at the Croatian consulate in the German city of Dusseldorf on Wednesday.
The bottles hit the front of the building. The flames were quickly extinguished and no part of the building caught fire, police said.
Passers-by grabbed the alleged thrower, 56, and held him until police arrived. Nobody was hurt in the incident.
Police said the man's motive was private rather than political and that he had acted alone. There was no evidence the Croatian national belonged to any political group, they said.