TUNIS - Some 100 people defied a government ban Saturday to rally in the centre of the Tunisian capital against Salafist extremism, accusing the authorities of double standards.

Security forces surrounded the demonstrators in Tunis as they shouted slogans calling for the government to resign.

Activists using the Internet had called the protest on the city's main thoroughfare, avenue Habib Bourguiba.

But the interior ministry, in a statement on its Facebook page, said the protest would be illegal because no one had asked for authorisation.

The ministry "reserved the right to react," the statement added.

But Fatma Ghorbal Lassoued, a leader of the Women and Dignity association behind the call, said the request for authorisation had been made according to the regulations on Tuesday.

"There are double standards. The supporters of the government and the Salafists can do as they please, but we have obstacles put in our way," she told journalists shortly before the rally.

Participants cited a Salafist gathering on May 20 at Kairouan in the west of the country and a pro-government demonstration outside the Tunis courthouse on Friday, which were allowed to take place.

Saturday's demonstration was called in response to violence last weekend in the northeast of the country, when radical Salafist groups attacked several police stations.

The ultra-conservative Salafists, some armed with clubs and swords, also burned down the shops of alcohol vendors who refused to close. They have been intensifying their attacks over the last 11 days.

On Thursday, responding to the attacks on the police stations, Interior Minister Ali Larayedh warned that police were authorised to use live rounds.

"The state of emergency is still in force and we will take all necessary steps to restore security in the country," he added.

On April 9, a demonstration on the same avenue went ahead despite having been banned but was violently broken up by the security forces, provoking widespread anger.

At least 15 civilians and eight police were hurt in the unrest.

Larayedh was summoned before parliament, and President Moncef Marzouki denounced the "unacceptable violence".

With the fall of president Zine el Abidine Ben Ali in January 2011, secular liberals and radical Islamists have been in constant conflict over whose values should prevail in the country.

Tunisians have also expressed deep concern over the rising power of Salafists since the revolution that toppled Ben Ali's regime and brought a moderate Islamist party to power.

The Salafist movement comprises several branches. Some adherents focus strictly on religion, some are politicians and some are jihadists who see violence as a legitimate means to impose their faith.

Researchers put the Salafists' numbers at around 10,000.