“I have decided from today to ban all union activity among security services in view of the danger that such activity represents for the security of the country,” he said at a press conference.
He was speaking as hundreds of Tunisian police officers, angered at charges of killing protesters, demonstrated outside the main government building in Tunis, security forces unions said.
They called for the immediate resignations of Interior Minister Habib Essid and army chief General Rachid Ammar. They accused the army chief of being behind recent unrest in Tunisia with the aim of seizing power.
At least two people have been killed and scores injured in recent violence in the centre and southwest of the country, prompting authorities to impose a curfew on three towns.
The police unions are in particular calling for a fair trial for 23 officers who have been detained on charges of killing protesters.
They were arrested in the wake of civil unrest in December and January which flared after weeks of protests initially focused on unemployment, sparked by the suicide of a young graduate who set himself alight on December 17 last year.
According to the union, 10 police officers were killed and 18 shot and injured on January 14, the day ousted president Zine El-Abidine Ben Ali was arrested as he attempted to flee the country.
Hated and feared during the Ben Ali regime, the police force feels it has been made a scapegoat for its excesses.
Caid Essebsi also pledged the “strict application of the state of emergency” decreed after the fall of Ben Ali and since prolonged by successive decrees, until November 31.
Tunisians are due to go to the polls on October 23 to elect a constituent assembly, which will draft a new basic law and road map for the north African country after more than two decades of autocratic and corrupt rule.
“The government will see the law applied,” the prime minister said, pointing out that it banned “all demonstrations, all strikes and all meetings that could affect the security of the country.”
“The minister of the interior has the right to place under house arrest any person known for activities affecting internal security,” he added.
“Many dangerous things happened in this country and that concerns all its citizens,” he said, adding that the government had met on Monday to discuss security measures.
Violence has in recent days rocked regions in the centre and southwest of Tunisia, claiming at least two lives and dozens of injured, and three towns have been placed under a nocturnal curfew.
Caid Essebsi accused unnamed “parties” of being behind the unrest and said, “It is astonishing that each time elections approach, denigration campaigns and trouble arise.
“The elections will take place on October 23. Our aim is to ensure that a transparent and free poll takes place for the first time in this country.”