South Africa's president says he is "seriously disturbed" by violent protests at some universities and is calling for calm on campuses nationwide.

President Jacob Zuma said in a statement Thursday that South Africans have the right to protest peacefully but must obey the law.

Students protesting for free education have clashed with police at several campuses in the past two weeks, forcing classes to be suspended in some cases.

Police on Wednesday fired rubber bullets during confrontations at Rhodes University in Grahamstown.