Police fired stun grenades to disperse students protesting at a Johannesburg university on Tuesday, as nationwide demonstrations over high tuition fees entered their third week.

Fewer than 100 students had gathered and started singing outside Wits University’s main hall before officers moved in to enforce a ban on public gatherings, said witnesses.

Police and private security guards in riot gear massed in the city-centre campus through the morning. Police said two students were arrested at Wits – full name, the University of the Witwatersrand – for public order offences.

Demonstrations over the cost of university education, prohibitive for many black students, have highlighted frustration at enduring inequalities in Africa’s most industrialized country more than two decades after the end of white-minority rule.

Protests first erupted last year, then subsided as the government froze fee increases and set up a commission to look into the education funding system.

The unrest boiled over again, closing some classes and universities, when the commission said on Sept. 19 that fees would continue to rise, albeit with an 8 percent cap in 2017.

“Following yesterday’s harassment of our staff, we have no choice but to deploy police around campus,” said university spokeswoman Shirona Patel.

She said the unversity, which shut down during the earlier protests, had reopened on Monday, but some students had forced some of the lecturers out of their offices.

University authorities across South Africa have warned that any further fee freezes could damage their academic programmes.

($1 = 13.6200 rand)