FACTBOX: What impact will South African violence have?

(Reuters) - A wave of xenophobic attacks spread through South African townships on Monday and police said at least 22 people had been killed since trouble broke out last week.

Below are answers to some questions about the unrest and its likely impact.

WHAT SPARKED THE TROUBLE?

Violence started on May 11 when mobs went on the rampage in Johannesburg's Alexandra township, targeting foreigners.

Perceptions that foreigners, mainly from Zimbabwe, Malawi and Mozambique, were behind robberies in the area sparked vigilante justice and foreigners were assaulted and driven from their homes.

The violence has now spread to many other areas around Johannesburg and also to the central business district, where scores of foreigners live.

There are an estimated five million illegal immigrants from other African countries in South Africa, at least three million of them from Zimbabwe.

WHY IS IT HAPPENING NOW?

Discontent has long been simmering in South Africa's poorest urban areas over inferior services, rampant unemployment, rising crime and perceptions that President Thabo Mbeki's government has failed the poor.

South Africa's economy, Africa's biggest, grew an average 5 percent for the past four years, but a boom since the end of apartheid has failed to create more jobs. Official unemployment is currently 23 percent but critics say the jobless rate is much higher.

Labor unions and the South African Communist Party have accused Mbeki and his senior officials of acting as little more than business agents for corporate South Africa -- still dominated by whites fourteen years after the end of apartheid.

WILL IT DRIVE THE IMMIGRANTS HOME?

The troubles are unlikely to force immigrants to return to countries where they face abject poverty or political violence.

The millions of Zimbabweans who have fled to South Africa did so to avoid starvation and escape the country's economic meltdown. They are unlikely to want to return to a country where basic commodities are in scarce supply, inflation is at 165,000 percent and unemployment is around 80 percent.

WHAT IS THE LIKELY FALLOUT FOR THE ECONOMY?

The violence has had no clear impact on the rand until now, but markets are watching closely. It is certainly expected to further dampen investor confidence.