TUNIS // An electro-dance craze that has gone viral on the internet is sparking insults and fisticuffs in Tunisia, where secularists and Islamists are battling for the soul of a nation.

The social divide in the North African country was sharply punctuated on February 6 when a lone hooded gunmen shot to death leading leftist opposition figure Chokri Belaid outside his home in the capital.

The authorities say the still-fugitive assassin was a Salafist Muslim.

A number of social media sites belonging to Salafists and other Islamist groups have denounced the Harlem Shake as indecent, with participants, some even dressed up as Salafists, smoking, dancing wildly and simulating sexual acts.

Yesterday saw more violence, but the worst injuries were probably only bruises and bloodied noses, when Salafists tried to prevent the filming of a Harlem Shake at a Tunis school.

At another school, south of the capital, students reacted angrily when their principal banned them from filming. They hurled stones at the police, who responded with tear gas.

When a dozen ultraconservative Muslim youths, some of them women, showed up at the Bourguiba Language Institute in Tunis's El Khadra neighbourhood, a Salafist bastion, students shouted "Get out, get out!"

One of the Salafists shouted: "Our brothers in Palestine are being killed by Israelis, and you are dancing." He said he wanted to explain what behaviour Islam considers as haram and halal.

That drew the ire of one youth, wearing the mask of a deformed face featured in the American horror film Scream.

"Mind your own business and keep your lessons of morality for others," he shouted. "No guy like you is going to stop us from doing what we want!"

Another Salafist, bearded and wearing military gear, was found to be carrying a petrol bomb, but was surrounded by teachers who prevented him from using it.

The incident degenerated into fisticuffs before the Salafists retreated.

Masters student and organiser Fidaa Jebali later showed an AFP correspondent a red welt on her cheek.

"One of the veiled girls called me an apostate before slapping me," said Jebali from behind huge rose-coloured spectacles. "It's not normal to have to suffer this in 2013."

In Sousse, 120 kilometres south of Tunis, students angered over their principal's ban "gathered outside the school, near a hospital, and began igniting smoke bombs," the interior ministry spokesman Khaled Tarrouche told AFP.

"The security forces tried to convince them to put out the smoke bombs, but they refused and threw stones at them and wounded two policemen. The forces of order were obliged to respond with tear gas," he added.

On Monday, the education minister Abdellatif Abid said a probe had been ordered into the staging two days earlier of a Harlem Shake by students in a Tunis suburb.

He said there could be expulsions of students or sacking of educational staff who were behind the staging of the dance.

The Saturday version was purportedly staged by students from Menzah 6 district in a school compound, with some in shorts and others sporting fake beards and the tunics typically worn by Salafists.