Officials in Tunisia's interior ministry said Friday they had banned a demonstration against Salafist extremism planned for this weekend, raising the prospect of fresh clashes on the streets.

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

But in a statement published on its Facebook page, the interior ministry said it was illegal because nobody had asked for authorisation.

The ministry "reserved the right to react," the statement 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 policemen were hurt, Interior Minister Ali Larayedh was summoned before parliament to explain what had happened and President Moncef Marzouki denounced the "unacceptable violence".

One group of activists insisted that they had filed a request for this latest demonstration on time.

Activists called for Saturday's "day of anger" protest 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, Larayedh warned that the police were authorised to use live rounds.

"Those who think that sovereign institutions such as police barracks can be attacked with impunity should know that in such cases the law authorises the use of live rounds," the interior minister told reporters.

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