Hundreds of anti-Islamist protesters clashed with police on Thursday outside the governor's office in the central Tunisian town of Gafsa, an AFP journalist reported.
The protesters, who were observing a symbolic funeral for Chokri Belaid, the leftist opposition leader assassinated on Wednesday, threw petrol bombs at the police, who fired large quantities of tear gas in a bid to disperse them.
The demonstration, in Tunisia's volatile central mining region was organised by the Popular Front, an alliance of leftist parties to which Belaid belonged.
It was the first unrest reported in Tunisia on Thursday, after violence the day before left one policeman dead in Tunis and saw protesters torch and ransack offices of the ruling Islamist Ennahda party in a number of towns, including Gafsa.
The phosphate producing region has a history of unrest, with an uprising against the regime of ex-dictator Zine El Abidine Ben Ali in 2008 brutally suppressed.
Separately, around 300 people marched down Habib Bourguiba Avenue in central Tunis, where clashes broke out with the police on Wednesday, calling for regime change.
"The people want the fall of the regime!" chanted the protesters as they headed towards the interior ministry, while the police, using loudspeakers, urged the protesters to remain peaceful and not throw stones.