"Those who were arrested have admitted they were pushed by former Ben Ali officials," he said. "Others said they were paid to do it."
A Reuters witness had earlier seen Tunisian soldiers fire into the air and use tear gas in an effort to disperse dozens of youths, many carrying sticks, who were breaking shop windows near Tunis's Barcelona Station.
The North African state's crime rates have soared since a popular uprising toppled Ben Ali on January 14, and security officials often say his supporters are trying to destabilize the country.
The clash followed a large protest late Friday against the make-up of the post-Ben Ali interim government. During that, security forces fired in the air to disperse protesters who burned tyres and threw rocks.
Prime Minister Mohamed Ghannouchi told Al Jazeera television police seized a car and its driver with $60,000 in cash which he said was being distributed to thugs.
"We have been facing a lot of difficulties lately, as if there is a ploy to destabilize the interim government ... Next week will be decisive in bringing about a road map" for a transition to democratic government, he said.
"The Tunisian people will decide on what will be done."
Critics of the interim government, which has promised to hold elections by mid-July, complain that it is too close to the old regime and has failed to provide adequate security.
Tunisia's revolution inspired a similar revolt in Egypt and sparked protests elsewhere around the Arab world, including in neighboring Libya.