Five Tunisian students said they went on hunger strike Wednesday against a ban on niqab veils imposed by a university, upping the ante in a dispute which began in November.

Mohamed el-Bakhti, spokesman of a group of ultraconservative Muslims from the University of Manouba's arts faculty, said the five were on hunger strike for an unlimited period in a "private place under medical monitoring."

The university at Manouba, 25 kilometres (15 miles) west of Tunis, had banned the garment, citing security concerns if the veil is worn with full-body garments.

But the group of Salafist Muslims had contested the ban, and held weeks of sit-ins at the university, forcing the faculty to shut for a month and a half and delaying examinations by three weeks.

El-Bakhti said the sit-in would go on alongside the hunger strike.

The faculty's dean, Habib Kazdaghli, told AFP on Wednesday that he would try to evacuate the protestors before January 24 examinations.

"We will be mobilised for this -- all the teaching staff, including retired professors, who will be here as volunteers to lend a strong hand during the examinations," he said.

Four classes were suspended Wednesday after the Salafists tried to get a niqab-wearing student into a class.

"Conditions will not be good for the examinations if this group acts with impunity on campus, hindering tests with their speeches, chants and prayers using loudspeakers," said Kazdaghli.

Meanwhile, violence also broke out between Islamist and left-wing students at the humanities faculty of Sousse university, about 140 kilometres southeast of Tunis. Three people were injured in the fracas.

A spate of protest actions is paralysing parts of Tunisia a year after the north African country's popular revolt sparked the Arab Spring uprisings.