Security forces used tear gas and shot into the air to disperse thousands of protesters in central-west Tunisia Wednesday, official and union sources said.

The trouble came on the day that members of Tunisia's interim government formally resigned, following the formation of the country's first-ever democratically elected constituent assembly.

The flashpoint was in Kasserine, 350 kilometres from Tunis, where thousands of residents protested that the "martyrs" from the town who died in the revolution which allowed the democratic moves to take place, were being forgotten, trade union leader Sadok Mahmudi told AFP.

The interior ministry confirmed the incident at Kasserine and said there was also some trouble at Thala et Feriana in the same area.