Riots over soaring food prices could not be ruled out in South Africa, the Congress of South African Trade Unions (Cosatu) said on Monday.

"We could not rule out similar riots [to those in other countries]in this country and that is why it was necessary to take the lead in channelling that anger into peaceful protests," said spokesman Patrick Craven.

The cost of basic foods has risen sharply around the world in recent months, sparking violent protests in many countries, including Egypt, Cameroon, Ivory Coast, Mauritania, Ethiopia, Madagascar, the Philippines and Indonesia.

"There are many people who feel very angry and need to give vent to their feelings especially in those cases where rising costs are not due to the global crisis but to price fixing and colluding," Craven said.

He said Cosatu wanted the entire food chain to be investigated. Farmers claimed that the price at which they sold their produce had no relation to the price in the supermarkets, he said.

"We want to know where the extra money is going, it is certainly not going to the workers. We know that."

The labour federation commenced with protests to draw attention to the rising food costs with a march through the streets of Polokwane on Sunday.

The protests would also focus on companies that had been found guilty of price fixing in Competition Commission rulings.

Cosatu would demand a reduction in the price of bread as a refund to customers for being overcharged and would ask for a zero value added tax rating on basic foods, as well as subsidies for the poor.

Craven said its campaign would gain momentum on Tuesday.

A march would take place in Gauteng on April 17 at 1pm to Eskom and Pick 'n Pay to protest against electricity and food prices. Memorandums would be handed over. Further details would be made available at a press briefing on Tuesday.

Protest marches were scheduled for May 17 in Mpumalanga. The campaign was set to start in the Western Cape on April 17 and in the North West on April 15.

Meanwhile, United Nations Secretary-General Ban Ki-Moon has warned that the rapidly escalating crisis of food availability has reached emergency proportions and threatens to wipe out seven years of progress in the fight against global poverty, the Associated Press reported.

He called for short-term emergency measures to meet urgent food needs and avoid starvation and longer-term efforts to significantly increase production of food grains.