Updated

Around 11,000 police officers and soldiers blocked an annual conference Sunday at Tunisia's main religious center by a radical Islamist movement that has been implicated in attacks across the country, prompting clashes with angry youths that resulted in one death.

Security checkpoints were in place and patrols conducted throughout the central city of Kairouan after authorities declared the conference to be held there by the ultraconservative Muslim group Ansar al-Shariah a threat "to security and public order."

Police clashed with stone-throwing young men in the center of the town and fired tear gas to disperse them. Kairouan hospital reported that five civilians and four policemen were injured in the clashes.

Far more serious, however, was a confrontation between police and supporters of Ansar al-Shariah in the low-income suburb of Ettadamon, north of the capital Tunis, where young men threw stones and burned tires and security forces responded with tear gas and warning shots.

The state news agency reported that a 27-year-old was killed in the clashes and 11 policemen injured.

The leader of Ansar al-Shariah, Seifallah Ben Hassine, is wanted for his involvement in a mob attack on the U.S. Embassy in September, and his followers have been accused of attacking art galleries, police stations and cinemas.

The robust response to the conference by security forces is unprecedented since the 2011 overthrow of President Zine El-Abidine Ben Ali, who presided over a strong police state.

The government, led by the moderate Islamist Ennahda Party, has long been accused by the opposition of being lax with attacks by ultraconservative Muslims, called salafis, on what they deem to be impious in the country.

Ansar al-Shariah's combative rhetoric, however, appears to have united the country against it. In a national dialogue conference involving unions, civil society and political parties Thursday, Ansar al-Shariah was widely condemned. The discovery of al-Qaida-linked militants in mountains along the Algerian border also alarmed people.

Alaya Allami, an expert on Islamic movements in Tunisia, said Ansar al-Shariah's more aggressive stance had resulted in a backlash in society and isolated it further.

The Tunisian army is hunting al-Qaida-linked militants in Tunisia's mountains of Jebel Chambi, and Allami said the operation "and the approach of elections have threatened these radical currents and caused them to try to impose themselves more on the social scene."

The spokesman of Ansar al-Shariah, Seifeddine Rais, was detained by authorities Sunday morning. Rais on Thursday said authorities would bear responsibility for any blood spilled if they tried to ban the conference.

Security has been high around Kairouan since Saturday, with police checking IDs and searching the cars of anyone entering the city.

Residents appeared to welcome the security and handed out roses to patrolling police, offering them encouragement.

Since the overthrow of Ben Ali in an uprising that heralded the region-wide Arab Spring, Tunisia's salafis have become increasingly aggressive about preaching their conservative version of Islam.

Last year's Ansar al-Shariah conference in Kairouan drew about 4,000 attendees and featured sword-waving horse riders and martial arts displays, along with a great deal of fiery rhetoric.