The widow of former president Nelson Mandela has warned the South African government to deal with the problems which have led to the recent xenophobic attacks or it will see them resurfacing again.

Speaking at the memorial service of Emmanuel Sithole, Graça Machel told mourners that since the attacks were happening for the second time, the nation had no excuse not to deal with them decisively.

"We may say that in 2008 we did not know. Now in 2015, we can no longer say we do not know. Now we know how bad it can be ... our actions have to be proportional to the deep crisis we are going through," Machel said.

Sithole was stabbed in Alexandra at the height of the xenophobic attacks that gripped the country. The men accused of his murder have since been arrested.

In a unique tone, calling herself "the mother of the nation" and "the most visible face of a foreigner", Machel said it was worrisome that in both the 2008 and 2015 xenophobic attacks, the main faces of the victims were Mozambicans.

She was referring to Ernesto Alfabeto Nhamuave, a 35-year-old Mozambican who was burned alive during the xenophobic violence in Ekurhuleni in May 2008. Sithole, another Mozambican, defined the heightened tensions of the 2015 xenophobic attacks.

"There is a message which I am yet to understand. Why does it have to be always a Mozambican face to symbolise the pain of South Africans, Zimbabwean, Malawians?" Machel asked.

The memorial service was held at the East Bank Hall in Alexandra and was attended by Sithole's family, the community of Alexandra, Johannesburg mayor Parks Tau and religious leaders.

Machel said the hatred in South African society was inculcated by the apartheid government. She warned that while the anger was expressed to foreigners for now, "tomorrow it will be against South Africans themselves".

The City of Johannesburg and the SA Council of Churches will cover the costs of the repatriation of Sithole's remains and funeral in his hometown in Mozambique.