The violence has unnerved investors and hit the rand currency. An overnight attack on African immigrants in Durban raised fears the unrest was spreading to other parts of South Africa from the Johannesburg area.

Essop Phahad, a senior aide to President Thabo Mbeki, told reporters that police, defence and justice departments were discussing whether to send troops to restive areas.

"We will await a report from them. Obviously, you're calling the army if the police is unable to cope. As far as I know, we are not there yet but we will await the report from our security cluster," Pahad said.

Many poor South Africans say the immigrants are depriving them of jobs and fuelling crime.

Local media in the eastern KwaZulu-Natal province said at least six African immigrants were injured in an attack on a Nigerian-owned tavern in the port city of Durban.

Police and provincial officials said the attack was not sparked by xenophobia, but it increased fears the violence could spread from the Johannesburg area where it erupted on May 11.

"There is a real fear that the violence will spread here," said Mary de Haas, who has been monitoring violence in KwaZulu-Natal since the 1980s. The province is home to South Africa's biggest ethnic group, the Zulus.

"There have been previous incidents in which foreigners were attacked," De Haas said.

The former wife of Nelson Mandela said the government had uncovered a plot to target rail commuters. Winnie Madikizela-Mandela is a member of the ruling African National Congress's national executive committee.

POLICE EQUIPMENT

Police have already asked the army for equipment to help combat the violence in shantytowns and black townships which has displaced thousands of people in South Africa's industrial heartland, a defence ministry spokesman said.

The United Nations' International Organisation for Migration said on Tuesday that the violence had displaced 13,000 people.

The attacks have prompted thousands of Zimbabweans, Mozambicans and other foreigners to seek shelter in churches, police stations and community centres. Criminal gangs are believed to be involved in the attacks.

South Africa's currency fell sharply on Tuesday, largely due to the violence. The rand was slightly firmer on Wednesday at about 7.66 to the U.S. dollar.

Government officials are worried the crisis could damage the lucrative tourism industry and cripple the nation's bid to host the 2010 soccer World Cup. An estimated half a million visitors are expected to visit during the tournament.

The violence has also increased political instability at a time of electricity shortages, rising inflation and disaffection among the poor over President Thabo Mbeki's pro-business policies.

ANC leader Jacob Zuma, the frontrunner to take over from Mbeki in 2009, has said there is no room for xenophobia in a country that dubs itself the "Rainbow Nation".

South Africa, with a population of about 50 million, is home to an estimated 5 million immigrants. Foreigners have been lured by work in mines, farms and homes and by one of the world's most liberal immigration and refugee policies.

The biggest group -- an estimated 3 million -- are from Zimbabwe. They have fled economic collapse at home and the violent political standoff since disputed March 29 elections.