Late last year, largely unnoticed in the west, Tunisia's president, Moncef Marzouki, gave an interview to Chatham House's The World Today. Commenting on a recent attack by Salafists – ultra-conservative Sunnis – on the US embassy in Tunis, he remarked in an unguarded moment: "We didn't realise how dangerous and violent these Salafists could be … They are a tiny minority within a tiny minority. They don't represent society or the state. They cannot be a real danger to society or government, but they can be very harmful to the image of the government."

It appears that Marzouki was wrong. Following the assassination of opposition leader Chokri Belaid last Wednesday – which plunged the country into its biggest crisis since the 2011 Jasmine Revolution – the destabilising threat of violent Islamist extremists has emerged as a pressing and dangerous issue.

Violent Salafists are one of two groups under suspicion for Belaid's murder. The other is the shadowy, so-called neighbourhood protection group known as the Leagues of the Protection of the Revolution, a small contingent that claims to be against remnants of the old regime, but which is accused of using thugs to stir clashes at opposition rallies and trade union gatherings.

The left accuses these groups of affiliation with the ruling moderate Islamist party, Ennahda, and say it has failed to root out the violence. The party denies any link or control to the groups. But it is the rise of Salafist-associated political violence that is causing the most concern in the region. Banned in Tunisia under the 23-year regime of Zine El Abidine Ben Ali, which ruthlessly cracked down on all forms of Islamism, Salafists in Tunisia have become increasingly vocal since the 2011 revolution.