A "gang" of around 60 people attacked the headquarters of a coalition of political parties opposed to Tunisia's ruling Islamists in Tunis overnight on Thursday-Friday, the opposition group announced.
"A paid gang tried to attack the headquarters of the Popular Front. There was no damage and our colleagues are fine... The cowards fled" when confronted by members of the leftist coalition, the group said on its official Facebook page.
It said 10 of its members managed to repulse "around 60" assailants, although Tunisian media said police intervened to stop the attack, with some people injured.
The police could not immediately be reached for comment and the identity of the assailants was not known.
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The Popular Front has a poor relationship with the ruling Islamist party Ennahda, and activists from the two groups often accuse each other of orchestrating political violence.
Tensions have risen since the assassination of a secular opposition MP at the end of July triggered a major political crisis that Tunisia's divided factions have failed to resolve.
Strikes and demonstrations erupted into violence on Wednesday, with some 50 policeman injured in clashes with protesters in the town of Siliana, and Ennahda's office was torched in Gafsa, another marginalised region plagued by social discontent.
The economic malaise and political deadlock gripping Tunisia has fuelled discontent nearly three years after the uprising that toppled former autocrat Zine El Abidine Ben Ali, along with a rise in attacks by Islamist militants, whom many accuse Ennahda of failing to rein in.
The Islamist-led government and the opposition agreed last month to negotiate an interim administration of independents as a way out of the current political impasse. But the talks were suspended shortly afterwards with the two sides unable to agree on a new prime minister.