The demonstrations have been going on for more than three weeks At least 35 people are said to have died in violent unrest in Tunisia, according to the International Federation of Human Rights Leagues, based in Paris.
The authorities have said only 14 people were killed in protests over unemployment at the weekend.
Unconfirmed reports suggest at least 50 were killed in Kasserine in three days.
On Monday, the government ordered all schools and universities to be indefinitely closed over the protests.
The head of the International Federation of Human Rights Leagues (IFHRL), Souhayr Belhassen, has said she had a list of 35 names, but the real number could be higher.
The IFHRL believes the death toll could be as many as 50, as does a Tunisian trade unionist, citing tolls issued by medical staff in a regional hospital in Kasserine.
“The number killed has passed 50,” Sadok Mahmoudi, a member of the regional branch of the Tunisian workers’ union UGTT, has told the AFP news agency.
Human rights campaigners say the violence has also spread from inland to several coastal towns important for Tunisia’s big tourism industry.
A trade unionist in the town of Thala told the BBC that police were warning residents not to gather in groups – even of two.
He said there was a desperate shortage of food and heating oil in the town.
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.
Demonstrations are rare in Tunisia, where there are tight controls aimed at preventing dissent.
The closure of schools is an indication of how seriously authorities are taking the demonstrations, which have been going on for more than three weeks, observers say.
President Zine al-Abidine Ben Ali has defended his government’s record in the face of the protests, and promised to create more jobs.
He says an extremist minority has been misleading the young, blaming gangs who were carrying out “terrorist acts”.
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.
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