Tunisia's new interior minister said some members of the security forces were in a "conspiracy" to undermine the state, after a wave of violence including the burning of a synagogue and an attack on the ministry itself.
Police also took former interior minister Rafik Belhaj Kacem, who was fired during violent unrest last month, into custody, his replacement Farhat Rajhi said on Tuesday.
Kacem, who had previously been under house arrest, was sacked two days before strongman former president Zine El Abidine Ben Ali was ousted and fled to Saudi Arabia amid growing unrest.
Gangs rampaged through schools in the capital on Tuesday, prompting the army to fan out to calm fears of chaos after the revolt that toppled Ben Ali.
Major street protests have dried up in Tunisia in recent days, after a reshuffle purged the interim government of most Ben Ali loyalists and appeased public opinion.
But sporadic acts of intimidation and sabotage have broken out after weeks of protests forced Ben Ali to flee the country on Jan. 14, ending 23 years of strict police rule.
Rajhi said some of the violence was part of an organized plot, after what he said was an attack by a 2,000-strong group on the interior ministry.
"These people who came yesterday to the ministry... are the same people who went out today to scare people," he told privately-owned Hannibal TV.
"There is a conspiracy against state security and there is a conspiracy in the security forces."
On Monday, youths armed with knives and sticks ran through the streets of Gassrine, burning government buildings and intimidating residents, the state news agency said.
The situation was partly aggravated by a police strike that began on Monday, but a deal was reached on Tuesday allowing security forces to set up a union to protect their rights.
Tunisia's interior ministry also replaced 34 senior security officials, a first step to overhauling the network of police, security forces and spies built up by Ben Ali over two decades.
Among those replaced were the head of national security, the head of general security and the head of presidential security, key positions under the old regime of Ben Ali.
Rajhi said he had sacked the national security chief because he had not followed orders in clearing out protesters camped outside government offices on Saturday. He questioned why no one was arrested following the attack on his own ministry on Monday.
Several political parties as well as the country's powerful labor union, whose offices have also been attacked, urged the government to bring the security situation under control to prevent the vacuum being exploited by Ben Ali loyalists.
Gangs of youths marauding through central Tunis on Saturday were chased away by vigilante shopkeepers, armed with knives and sticks, who said they were protecting their businesses.
Some shopkeepers suggested the gangs were either loyalists of the former ruling RCD party or paid by Ben Ali to create havoc in the streets.
The interior minister's comments came hours after a U.N. human rights official said Tunisia's security forces must be overhauled to stop them from working against the people as they did during the uprising, in which 147 people were killed.
Bacre Waly Ndiaye, leading an eight-member team sent to Tunisia by the U.N. High Commissioner for Human Rights, told a news conference that 510 people had been wounded during the weeks of protests that began on Dec. 17 and inspired a massive popular uprising in Egypt.
Tunisia's interim government has promised to investigate any deaths and injuries that took place during the uprising and has begun to compensate the families affected.
The government has also promised to take back the assets held by Ben Ali and his family in Tunisia and abroad.
French authorities seized a small aircraft belonging to Ben Ali's family at an airport near Paris, the prosecutor's office said on Tuesday.
The move comes a day after the European Union agreed to freeze assets belonging to Ben Ali and his wife.
Ben Ali and his family built up interests in many Tunisian companies and industries during his two decades in power, including hotels, banks, newspapers and pharmaceutical firms.
Many of those firms are listed on the Tunisian bourse, which reopened on Monday.
Earlier on Tuesday, a new interim government to review Tunisia's tense security situation.
It was the first meeting of Prime Minister Mohammed Ghannouchi's government since it was reshuffled on January 27.
A government source, speaking on condition of anonymity, said the meeting was focusing on security developments around the country. Monday.
The source said a lifting of the a dusk-to-dawn curfew imposed January 13 appeared premature as "the situation is not yet stabilized."
Separately government spokesman Taieb Baccouche announced Tunisia would endorse four major human rights protocols, including the Rome statute which created the International Criminal Court.