UPDATE 4-SAfrican rail and port workers in national strike
* Rail and port workers strike to push pay demands
* Protest watched closely as World Cup approaches
* Fuel and commodity producers make contingency plans
(Adds violence, paragraphs 5-7)
JOHANNESBURG, May 10 (Reuters) - Thousands of South African transport workers went on strike on Monday at logistics group Transnet [TRAN.UL], threatening to cripple rail, fuel pipelines and port operations in Africa's biggest economy.
The strike -- the latest in a series of public protests before next month's World Cup soccer tournament -- could affect coal and iron ore exports, fuel distribution, and shipping.
Power utility Eskom said the strike, which began after wage talks broke down, would have no impact on the transport of coal used to power its plants, since only small amounts of coal were carried by rail, with the rest supplied by conveyor belts directly from mines. [ID:nLDE6461KZ]
Transnet does not run passenger train services.
The company said strikers at one of its units in the port city of Durban left the agreed picket area, forced their way into Transnet's premises and assaulted and stripped naked other staff at work.
Police fired rubber bullets to restore order, Transnet said.
"Twelve people were injured and six are now in hospital," the company said in a statement. "Transnet is pressing criminal charges against the perpetrators of violence."
The South African Transport and Allied Workers Union (Satawu) said it expected all of its 20,000 members to strike.
Another union, the United Transport and Allied Trade Union (Utatu), urged its members to consider Transnet's latest pay offer and to report for duty on Monday.
If Utatu's members reject the offer, the union said it would join the strike by Wednesday. The two unions represent 85 percent of Transnet's workforce of about 54,000 people.
Both unions want a 15 percent pay increase. Transnet has now offered 11 percent. "We can keep this strike going as long as the employer has not met our demands," said Joseph Dube, Satawu's secretary for KwaZulu Natal province.
Fifteen people were hurt when police fired rubber bullets at them in Durban after they failed to follow a police order to disperse, the SAPA news agency said.
Transnet and coal, iron ore, ferrochrome and fuel producers said they were confident they could supply customers for days due to built up stocks at the ports.
Anglo American Plc's (AAL.L) thermal coal unit, the country's biggest coal exporter, was not affected. South Africa exports most of its coal to power stations in Europe and Asia.
For now, operations at Richards Bay Coal Terminal, the world's largest coal export terminal, have been running as normal, Chief Executive Raymond Chirwa said. "Depending on ship arrivals, our stocks could last us for 3-4 weeks," he said.
Anglo unit Kumba Iron Ore (KIOJ.J) said it had enough stocks at Saldanha port to load vessels for at least seven days.
If the strike is prolonged, it could impair the country's ferrochrome industry, the world's largest. Hernic Ferrochrome, a unit of Japan's Mitsubishi Corporation (8058.T), relies on Transnet for 75 percent of its transports.
Freshgold SA Exports, which ships fresh produce out of the country said its operations were being hit.
"The strike has physically halted our container loadings from this morning ... if it's a week the impact will be quite severe," said Freshgold Managing Director Pieter von Maltitz. (Additional reporting by Shapi Shacinda, Olivia Kumwenda, Mary Theru; Editing by Mark Heinrich)