Tunisian Prime Minister Ali Larayedh speaks during a press conference at the Government Palace in Tunis, Tunisia, Aug. 27, 2013. (MOHAMED MESSARA/EPA)

Tunisia’s prime minister on Tuesday described an ultraconservative Islamist group implicated in last year’s U.S. Embassy attack here as a terrorist organization with links to al-Qaeda.

Ali Larayedh said at a news conference that the Salafist group Ansar al-Sharia is considered a terrorist organization based on seized documents, confessions and weapons captured from group members. The designation means that membership in Ansar al-Sharia is now a crime.

“There will be no respite in the struggle against terrorists and against those who take up arms against the citizens and institutions of the state,” he said. “We will ensure Tunisians have a future characterized by freedom and well-being.”

The group is believed to have helped to orchestrate an attack last September on the U.S. Embassy by protesters angry about a U.S.-made video mocking Islam; four assailants were killed in the clashes.

The government has also said that members of the group were involved in the assassination of two opposition politicians this year and are cooperating with militants fighting the army in the mountainous Jebel Chaambi region along the Algerian border.

The group’s leader, Seifallah Ben Hassine, fought the Soviets in Afghanistan and was later imprisoned by the former Tunisian government until his release after the revolution that overthrew the secular dictatorship. He is once more in hiding.

Larayedh urged members of the group to quit or face prosecution.

After the overthrow of the autocratic leader Zine el-Abidine Ben Ali, religious groups flourished in Tunisia with the election victory of the moderate Islamist Ennahda Party and the rise of conservative Salafist groups calling for greater piety in society.

Many of the Salafi groups resorted to violence and intimidation to push their views and included former militants in their ranks. After being accused by the opposition of turning a blind eye to the Salafists’ excesses, the Islamist-led government finally moved to confront them.

Ansar al-Sharia’s annual conference was banned in May, provoking clashes between police and the group’s supporters.

Tunisia is the birthplace of the Arab Spring and home to a relatively educated population, and its transition to democracy is being closely watched. The process has stalled following the latest political assassination in July and nearly a third of the members of the elected assembly have withdrawn, calling for a new technocratic government. There have been fears that the transition could be derailed, as happened in Egypt.

— Associated Press