Correctional Services spokesman Manelisi Wolela has denied allegations that student leader Mcebo Dla.
Xenophobia is on the rise in South Africa, where foreigners are increasingly being blamed for spiralling crime and growing unemployment.
Africa's largest economy started welcoming foreigners after the demise of apartheid in 1994, but the public mood is turning hostile.
The government of Africa's youngest democracy is also tightening immigration laws, the head of the Human Rights Commission said.
"Xenophobia is definitely increasing," the commission's Jody Kollapen said.
"In the post-1994 era there was a massive inflow from all parts of Africa. Xenophobia started manifesting itself, but excluded those who came from Europe because of the classic apartheid stereotyping that saw whites as people who bring in skills, money and investment and the others as threats."
In the late 1990s some immigrants were killed on a train by South Africans. Lately, hate attacks have tended to target Zimbabweans and Somalis. South Africa welcomed nationals from Mozambique, Angola, Zimbabwe and Zambia because they had backed the ANC during the liberation struggle. But that's changing.
"Increasingly there is a feeling that though we appreciate what they did, we cannot remain eternally obliged," Kollapen said, adding that the high unemployment rate exacerbated the situation. The alarming crime rate is blamed by many on foreigners.
"The myth is that Nigerians are into drugs and prostitution, Zimbabweans into cash heists, and Mozambicans break into houses," he said.
Nigerian-born Enyinna Nkem- Abonta, a ruling party MP, felt the bite during a heated debate when he was in the opposition after a serving minister asked him why he had "run away" from his own country.
Nkem-Abonta, a French-trained economist, said he did not get a senior job at a parastatal firm because of his Nigerian roots. But he does not blame South Africans.
"If the pie was expanding, people wouldn't care too much. The government has to educate them that immigrants are productive.
"We have South African ministers saying they want our professionals, [but] they make visa procedures tighter for our people. If this goes on, it will be tit-for-tat," an Asian diplomat said.
Ivory Coast national Etienne Gaba is enraged at being the butt of threats, intimidation and insults.
"South Africans forget that it is their population of foreign descent that catapulted this country to being the continent's superpower."
Muneer, a Bangladeshi restaurateur in Johannesburg suburb, echoes him.
"I saw a business opportunity where no South African saw one. I set up this place and I employ 34 people, including some locals.
"And yet they accuse me of kicking them in the stomach," he said. - Sapa