By Laura Clarke and Devon Maylie

Platinum prices rose to their highest level in four months Wednesday as spreading labor unrest in South Africa raised the possibility that a further 40% of world production of the metal could be affected by a dispute that has already shut down significant output.

South Africa, which accounts for 75% of world platinum supply, has been roiled by violent clashes at three of its four leading platinum mines this year. Fears that a near two-week standoff between workers and bosses at Lonmin PLC's (LMI.LN) Marikana mine could spread to the world's biggest platinum producer, Anglo-American Platinum Ltd. (AMS.JO), or Amplats, had likely underpinned the price move, traders and analysts said.

Platinum hit $1,526 a troy ounce Wednesday morning, its highest level for 15 weeks, before slipping back to trade at $1,512.50/oz at 1059 GMT.

"The risk of contagion of the South African tensions will have sent short positions running for cover. It doesn't look like the situation is going to be secured overnight," said a London-based trader.

Amplats workers Wednesday became the latest group of platinum miners to demand higher wages, following similar requests by employees at Lonmin, Impala Platinum Holdings Ltd. (IMP.JO) and Aquarius Platinum Ltd. (AQP.AU, AQP.LN). Rock drill operators at Royal Bafokeng Platinum Ltd. (RBP.JO) have also made similar wage demands, local media reported Wednesday.

The situation has been most severe at Lonmin's Marikana mine, where 44 people have died in violence since trouble broke out on Aug. 10. The dispute has riven public opinion in South Africa and escalated a growing rivalry between the country's two largest mine unions.

Until today, Amplats was the only one of the country's top four primary platinum producers to have been unaffected by serious labour disputes. Amplats said Wednesday that, despite the demand from some workers for higher wages, there have been no stoppages or strike threats.

The longer-running disputes at Impala, Lonmin and Aquarius have all forced the companies to shut down some output.

The trouble has caused platinum prices to rebound, after they slackened in recent months as demand from the world's auto makers became weak. ABN AMRO said Wednesday that if the labor tensions remain unresolved, "a further out performance of platinum is on the cards."

Analysts said the labor dispute could also have an impact on sentiment towards the country's currency, the rand, which was weaker Wednesday after a strong rally Tuesday.

"On the whole we consider the South African currency's appreciation potential to be limited short term as the recent escalation of a protest at a platinum mine negatively affected investor confidence," said Commerzbank.

-Write to Laura Clarke at laura.clarke@dowjones.com and Devon Maylie at devon.maylie@dowjones.com (Alex Macdonald and Alexandra Fletcher in London contributed to this report.)

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