A protester was shot dead and several people injured in Tunisia after security forces opened fire during violent clashes, officials said.
The officers opened fire after coming under attack with Molotov cocktails thrown by the crowd, they said.
Several members of the security services suffered severe burns.
The demonstration in the central town of Menzel Bouzaiene took place in a region reportedly gripped by tensions over youth joblessness.
Agence France-Presse news agency quoted an unnamed interior ministry official as saying: "The groups involved in these acts of violence and trouble encircled and attacked a national guard post by throwing fire bombs and stones."
After attempting to disperse the crowd by firing warning shots, security forces opened fire in self defence, he added.
"This incident led to one death and two injured among the attackers. Several national guard agents suffered burns, including two who are in a coma," a government statement said.
A student representative, Mohamed Fadhel, said the man who died was 18-year-old Mohamed Ammari.
Mr Fadhel said the protesters had also set fire to police cars, a train engine, and the local headquarters of the governing Constitutional Democratic Rally party.
He said police had surrounded the town and were not letting people travel in or out, and that many arrests had been made.
Tensions have been simmering in the region, Sidi Bouzid, since the attempted suicide last week of a 26-year-old graduate, Mohammed Bouazizi, who sold fruit and vegetables because he could not find a job.
The Tunisian League for the Defence of Human Rights said he doused himself in petrol and set himself alight when police confiscated his produce because he did not have the necessary permit.
Demonstrations followed and tensions heightened when another young man electrocuted himself, saying he was fed up with being unemployed.
The government said the violence was isolated and had been exploited by the opposition. However, Development Minister Mohamed Nouri Jouini travelled to the region on Thursday and announced investment in an employment programme.
The BBC's Magdi Abdelhadi says public protests in Tunisia are rare and political dissent is repressed, while the government is often criticised for its human rights record.