Spanish police searched for possible explosives at the Madrid headquarters of the ruling conservative Popular Party after a man rammed his car into the office entrance.
No one was injured in the early morning incident. Spanish national police spokesman Antonio Nevado told Spanish radio that the attack did not appear to be terrorism-related. The driver of the car was arrested.
Mr Nevado said bomb disposal experts searched the area in and around the office in central Madrid.
He said two gas cylinders had been found in the car and that police were also analysing other material found in the vehicle.
Spanish police said the suspect had financial problems.
The city’s central street was sealed off for four hours, causing major disruption to traffic.
Demonstrators often protest near the ruling party’s headquarters about corruption scandals or the government’s handling of Spain’s economic crisis.
PA