Graca Machel, widow of Nelson Mandela, has appealed for African unity at a memorial service for a victim of recent xenophobic violence in South Africa.

Ms Machel called Mozambican Manuel Jossias' murder "a symbol of what must not happen again".

In an emotional speech in Johannesburg, she said the recent violence should be "a wake-up" call for the entire region.

At least seven people have died over a month of attacks on foreigners and foreign-owned property in South Africa.

To loud applause from the crowd, Ms Machel, who is a former first lady of both South Africa and Mozambique, encouraged acceptance of all nationalities:

"I am South African. I am Mozambican. I am Zambian. I am Zimbabwean," she said, continuing:

"Migration is in our blood! The borders were created by colonisers. They mean nothing to us because we are one."

Ms Machel described the recent violence as an "expression of self-hate which was inculcated by the system of apartheid".

She stressed that similar attacks would happen again unless countries throughout the region were able to provide better economic opportunities for their people.

After her speech, the former first lady broke down in tears, reports the BBC's Milton Nkosi from the scene.

Ms Machel, 69, was married to Samora Machel, the first president of independent Mozambique, who died in a 1986 plane crash.

She married Mr Mandela on his 80th birthday, in 1998.

Speaking on behalf of the family, Mr Jossias' cousin Veronica Sithole told the congregation that he had been the breadwinner for the whole family.

"You are robbers because you left us broken. You are evil. You didn't hear him pleading for mercy," she said, addressing his killers directly.

Mr Jossias was clubbed and stabbed to death in the Alexandra township of Johannesburg on 18 April.

His murder, which was was captured on camera by a photojournalist, shocked the nation and caused global outrage.

Initially, he was referred to in the media as Emmanuel Sithole, but South African President Jacob Zuma has since confirmed his real name as Manuel Jossias.

"He used a false name to avoid detection by authorities as he was an illegal immigrant", said the president in his freedom day speech on Monday.

The president also used his speech to criticise irregular migration from other countries in the region:

"As much as we have a problem that is alleged to be xenophobic, our sister countries contribute to this. Why are their citizens not in their countries and are in South Africa?" he asked, in comments reported in local media, but not included in the official government transcript of his speech.

Four suspects appeared in court last week over Mr Jossias' killing. The case has been adjourned until 4 May.

Mr Jossias in not currently included in the government's official count of victims of the recent xenophobic violence.