A regional office of Spain's leftist Unidas Podemos party was hit by a fire-bomb attack on Friday, police said.
The attack took place in Cartagena in southeastern Spain. The blaze damaged the exterior of the building.
Podemos accused right-wing elements of carrying it out.
"The street terrorism of the far-right will not intimidate us," party leader Pablo Iglesias, who is standing as a candidate in regional elections in Madrid on May 4, said on social media.
Police said no arrests had been made after the attack, which took place in the early hours of Friday morning.
It was the sixth time vandals have struck at the party building, a Podemos spokesman said.
(Reporting by Graham Keeley, Elena Rodriguez; Editing by Angus MacSwan)
