Fresh protests have broken out in a suburb of the Tunisian capital, Tunis.
Police reportedly fired into the air to disperse protesters in Ettadamen, 15km (9 miles) from the city centre, where soldiers have since been deployed.
The government has said 21 people have been killed in the recent unrest, though union and health officials have said the toll may be at least 50.
The most serious protests in Tunisia for decades have been sparked by anger at unemployment and social inequality.
The unrest prompted the government to deploy troops in the centre of Tunis on Wednesday.
On the city's main avenue, two military vehicles were parked opposite the French embassy, and armed soldiers were on patrol, according to the Reuters news agency.
Troops were also reportedly deployed at major intersections and outside the state television headquarters.
Late on Tuesday, youths threw stones at police and vandalised shops, cars and a government office in the working-class suburb of Ettadamen.
Security forces responded by firing tear gas and shots into the air.
"We are not afraid, we are not afraid, we are afraid only of God," the demonstrators chanted.
The government said four civilians had been killed by police who acted in self defence in the town of Kasserine. But local residents say the protesters were shot dead by police snipers on rooftops.
Meanwhile, Swiss police are investigating an attempt to set fire to the Tunisian embassy in Berne. The fire failed to ignite and no-one was hurt.
An anti-government protest was also held outside the embassy in Paris.
On Tuesday evening, Communications Minister Samir Laabidi gave the government's latest death toll.
"Our numbers say there are 21 dead," he said, denying reports of a higher number of casualties.
"Those who have spoken of 40 or 50 dead should produce a list of names," he said.
He also reiterated the government's claim a fringe movement of extremists was fomenting violence, saying that "religious extremist movements and extremist movements from the left" were behind it.
The government would respond with "economic and social reforms and more opening up towards liberty", he said.
The protests began after Mohamed Bouazizi, a young unemployed graduate, set himself on fire on 17 December because he had been prevented from selling vegetables in the town of Sidi Bouzid without a licence. He later died from his injuries, and there have been several other suicides linked to the protests.
A further two people died earlier in the unrest.
Demonstrations are rare in Tunisia, where there are tight controls aimed at preventing dissent.
This week the authorities ordered the closure of all schools and universities amid the continuing demonstrations - an indication of how seriously they are taking them.
President Zine El Abidine Ben Ali has defended his government's record in the face of the protests, and promised to create 300,000 jobs before the end of 2012.
But the Tunisian government's response has been criticised by the EU and the US, which has called on the country to respect freedom of expression.
In its strongest statement on the violence to date, US state department spokesman Mark Toner said it was "deeply concerned by reports of the use of excessive force by the government of Tunisia".
Mr Ben Ali is only Tunisia's second president since the country gained independence from France in 1956.
He came to power in 1987 and was last re-elected to a five-year term in 2009 with 89.62% of the vote.