Police during the weekend fired tear gas and used batons against protesters defying a government ban on demonstrations. Amna Guellali, a researcher for Human Rights Watch, said members of the opposition were among those roughed up by police.
"There was a feeling of 'We are going to defy this ban just as we did during Ben Ali's rule,'" she was quoted by The New York Times as saying.
Former Tunisian President Zine el-Abidine Ben Ali, who fled last year to Saudi Arabia, faced trial in absentia for his alleged role in the deaths of protesters during the country's Jasmine Revolution in January 2011.
At least 250 people died during the revolution seen as sparking the so-called Arab Spring last year.
In March, the Tunisian Front of Islamic Associations called for demonstrations to implement Shariah, or Islamic, law in post-revolution Tunisia. Later, Human Rights Watch called on the country's constituent assembly to draft a constitution that respects international human rights law as part of domestic law.