The government has now deployed army forces to protect public buildings which have become targets for protestors.
The protests broke out after activists and politicians denounced increases in Value-Added Tax and the introduction of social contributions at the start of the year as a tough new budget was implemented.
Warda Atig is one of the founders and spokespeople for the Fech Netannew - What Are We Waiting For? - campaign, which had organised Friday's protests.
Interior ministry spokesman Khalifa Chibani said 151 people were arrested Thursday, taking the number detained for alleged involvement in the violence to 778 after several nights of unrest.More news: HBO's first teaser for Fahrenheit 451 burns everything down
In December, unemployed protesters and activists marched through the streets of Sidi Bouzid, angry over the lack of jobs and opportunities that continue to plague residents. The UN said it was concerned about the number of arrests during the protests.
"The perpetrators want to sow dissension between Jewish and Muslim communities living in harmony on the island for many years", Trabelsi said.
More than 770 people have been detained in almost a week of sometimes violent demonstrations.
"We call on the authorities to ensure that people are not arrested in an arbitrary manner and that all those detained are treated with full respect for their due process rights and are either charged or promptly released", he said.More news: India Willoughby was sexually attracted to a DALEK
Tunisia's main opposition Popular Front had called for demonstrations through the week.
The government has blamed the opposition and "troublemakers" for stoking unrest, a charge the opposition has denied.
Tunisia appears to have little scope to back away austerity.
While Tunisia is widely seen as the only democratic success story among "Arab Spring" nations, it has also had nine governments since the overthrow of Zine El-Abidine Ben Ali, none of which have been able to deal with growing economic problems.More news: Zac Brown Band to play Blossom Music Center this summer
Protests are common in Tunisia in January, when people mark the anniversary of the revolution that ousted long-time dictator Ben Ali.