Partisans of Tunisia's Islamist ruling party attacked a hotel on Saturday where members of a secular opposition party met to commemorate the alleged murder of one of their officials, an AFP correspondent said.
Hundreds of demonstrators brandishing banners hostile to the opposition party Nidaa Tounes gathered outside Hotel Midoune, on Djerba island, where the meeting was being held, the correspondent said.
The meeting marked the end of 40 days of mourning for the death of Lotfi Naguedh, who the party claim was beaten to death in October during a demonstration in the southern city of Tataouine.
Some demonstrators threw rocks at officials of the opposition party and later broke through a police and military cordon, besieging the entrance to the hotel and threatening to attack if the opposition officials were not expelled.
Nidaa Tounes (Call of Tunisia), founded in July and led by former premier Beji Caid Essebsi, is accused by Tunisia's ruling coalition of regrouping former regime officials and seeking to undermine the government.
Its supporters regularly clash with backers of the ruling Islamist Ennahda party.
Since the summer, violent demonstrations and attacks by radical Islamist groups have increased across Tunisia, which is struggling to stabilise since the revolution that ousted former despot Zine El Abidine Ben Ali two years ago.