As the United States said it was "deeply concerned" by reports that authorities had used excessive force against protesters, police broke up fresh demonstrations by Tunisian intellectuals aimed at condemning the crackdown.
"Our numbers say there are 21 dead," Communications Minister Samir Laabidi told a news conference, denying the reports of a higher death toll.
"Those who have spoken of 40 or 50 dead should produce a list of names," he said.
Officials had previously given a toll of 18 dead.
"We regret the deaths and sympathise with the families," Laabidi said.
"All peaceful demonstrations are tolerated, logical and understandable," he said, adding however that "violence threatening security and stability" crossed a "red line".
"Police never fired on protesters, these deaths occurred during attacks and acts of vandalism against public buildings, police stations or schools," he said, accusing "Islamic and left-wing extremists" of manipulating protesters.
Meanwhile fresh clashes between protesters and security forces broke out Tuesday night in Ettadhamoun, a suburb of the capital Tunis, residents told AFP.
Groups of young protesters burned a bus and looted businesses and a bank, shouting "We are not afraid!", one witness said.
Witnesses said police could be seen firing tear gas at the protesters and shots could be heard.
Violence had earlier erupted overnight in the central town of Kasserine where locals alleged gunmen on rooftops shot at protesters but authorities accused rioters of attacking police.
The United Nations and Europe called for restraint and State Department spokesman Mark Toner said Washington "is deeply concerned by reports of the use of excessive force by the government of Tunisia."
Groups of artists, actors, lawyers and journalists tried to demonstrate Tuesday against the harsh crackdown but were prevented by security forces, they said.
"We wanted to peacefully express our anger and our indignation," theatre employee Fadhel Jaibi said after police broke up a gathering outside the municipal theatre against "violence and excessive use of force".
"We wanted to demonstrate to say stop killing people, to condemn obstacles preventing journalists from reporting freely on the unrest in the country," said Neji Bghouri, former president of the National Union of Journalists.
Staff at the regional hospital in Kasserine, 290 kilometres (180 miles) south of Tunis, meanwhile halted work for an hour to condemn the high number of victims.
"It is chaos in Kasserine after a night of violence, of sniper firing and pillaging," said Sadok Mahmoudi from the regional branch of the Tunisian General Union of Labour (UGTT).
"The number killed has passed 50," he said, citing figures issued by medical staff in the town's hospital for the past three days.
The Paris-based International Federation for Human Rights said at least 35 people were killed on Saturday and Sunday in Kasserine and nearby Regueb and Thala -- remote, farming areas with high rates of youth unemployment.
"The total figure is higher. It's somewhere around 50, but that's an estimate," its president Souhayr Belhassen told AFP, adding there were so many wounded that "they can't be counted".
The rare wave of protests was unleashed by the December 17 suicide of a 26-year-old graduate who set himself on fire after police prevented him from selling fruit and vegetables to make a living.
Another suicide was reported Tuesday in the same area, central Sidi Bouzid, with relatives of a 23-year-old unemployed university student saying he had electrocuted himself. It was the fifth suicide linked to the protests.
Tunisia's unemployment rate is officially 14 percent, but the percentage of graduates without work is about double that.
In a bid to address the concerns, President Zine El Abidine Ben Ali announced in a televised address Monday the creation of 300,000 jobs on top of 50,000 already pledged for the regions, but branded the protesters "gangs of thugs".
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