Larayedh said around 200 Salafists were arrested and vowed firm action against the group considered close to Al-Qaeda that he linked for the first time to "terrorism," prompting analysts to see a possible shift in government policy.
"Those proven to have nothing against them will be released, but those found to have been involved in violating the law will be prosecuted," he told AFP during a visit to Doha.
"Ansar al-Sharia is an illegal organisation which defies and provokes state authority," Larayedh told Tunisian state television.
"It has ties to and is involved in terrorism," added the former interior minister and stalwart of the ruling Ennahda party.
His moderate Islamist party has been sharply criticised for failing to prevent a surge in attacks by hardline Islamists since the mass uprising that toppled Zine El Abidine Ben Ali, and of being too lenient towards the Salafists.
But faced with the threat of two armed jihadist groups hiding near the Algerian border, it has hardened its stance, banning the Salafists' planned congress on Sunday in the holy city of Kairouan after their leader threatened "war" against the government.
Defying the ban, the Salafists gathered instead in Ettadhamen, a poor Tunis suburb, where clashes erupted as the police moved in, leaving at least one protester dead and 15 police hurt.
The neighbourhood was calm on Monday, but Ansar al-Sharia and a police source said a second person had also been killed in the violence.
Interior ministry spokesman Mohamed Ali Araoui, meanwhile, told reporters that on May 16 a "terrorist cell was dismantled" in the Kairouan region and "a 23-year-old who planned to attack the police and army had been arrested."
Tunisia's secular opposition, normally outspoken critics of Ennahda, said it "welcomes" the government's firmness towards the Salafists.
The Republican Party number two Issam Chebbi praised the interior ministry's decision "to impose respect for the law and for the state," and called for a "national strategy to confront fundamentalism and terrorism".
Analysts said the premier's comments late on Sunday could signal a turning point.
"It is a change of language. Larayedh has never before used this term for Ansar... reserving the word terrorist for the groups" which being hunted on the Algerian border, said Michael Ayari from the International Crisis Group think tank.
He said it remained to be seen whether Larayedh's words would translate into actions, pointing out that dozens of Salafists were arrested after an attack on the US embassy last year and most were freed several months later.
"The words count, but we still can't say that the policy has changed, that they mark a point of no return, and that the Ansar al-Sharia activists will now be arrested for belonging to the movement."
Ansar al-Sharia's leader Abu Iyadh, meanwhile, was defiant in a message posted online on Sunday.
"God knows well that I would like to have been with you at the moment when you opened a shining page in the history of our nation. You have shown the entire world that your efforts cannot be defeated despite the persecution of your leaders," he said.
The former Al-Qaeda fighter in Afghanistan, whose real name is Saif Allah Bin, has been on the run since September, after the attack by Islamist protesters on the American embassy in Tunis that he is accused of having orchestrated and which left four assailants dead.
Salafists, who advocate an ultra-conservative brand of Sunni Islam, benefited from the regional security vacuum that accompanied the Arab Spring uprisings.
Ansar al-Sharia is considered the most radical of the extremist groups to have emerged in Tunisia since the 2011 revolution.