The headquarters of Spain's Podemos (United We Can) party was attacked on Friday morning by unknown assailants who reportedly firebombed the building.
Footage posted on the left-wing party’s Facebook page showed the building in Cartagena, Murcia in flames, with its windows sprayed with obscene graffiti.
Podemos, an anti-austerity and pro-democracy movement, described the incident as “Fascist terrorism” on social media and said its offices had previously been daubed with the word “Redes” ("reds").
It added: “If we are to preserve freedom and democracy, we must stop the path of the far-right and those who whitewash it.”
Party leader Pablo Iglesias, who is a candidate for the elections of the Community of Madrid on May 4, has also blamed the “extreme right” for the attack. "The street terrorism of the ultras is not going to intimidate us,” he wrote on Twitter.
In a statement on Friday afternoon, local coordinator Javier Sánchez Serna said the Cartagena branch had been targeted in three separate attacks since last May. He also criticised the country's right-wing parties PP and Vox for not condemning the previous incidents.
The latest attempt, he said, “to set fire to the headquarters with Molotov cocktails… could have caused real human misfortune and not only material damage."
No-one is thought to have been injured in the incident. Podemos Cartagena filed a complaint with the National Police on Friday morning.