Johannesburg. Thousands of mine workers have downed tools at South Africa’s Lonmin mine after a union leader was shot dead in the restive platinum belt at the weekend, a company official said."Lonmin operations are suspended this morning due to an illegal work stoppage,” Sue Vey, a spokeswoman for Lonmin, told the AFP news agency on Tuesday, adding that work had stopped at all of the firm’s 13 shafts in the northwestern Rustenburg mining town.Al Jazeera’s Tania Page, reporting from Johannesburg, tweeted that Lonmin management were unsure about the motives behind the strike, but that protests were peaceful.The workers were singing and dancing on the streets, according to a witness.The strikes come amid growing union rivalry in the region where 34 miners were last year gunned down by police during a wildcat strike at Lonmin’s Marikana mines.Last Saturday, four unidentified men killed a mining union leader Mawethu Steven as he was watching football in a bar in Rustenburg.Steven was a member of the Association of Mineworkers and Construction Union (AMCU) which has recorded growing membership at the mine.The union leader was due to testify at a judicial inquiry into last year’s killings by police of striking mineworkers, an incident which shocked the world and brought back memories of apartheid police brutality.Meanwhile, the National Union of Mineworkers (NUM), a rival union, alleged the striking workers were intimidating its representatives. "There is intimidation and violence. They are singing and dancing and have blocked roads,” the group said."Cars are being turned away. It’s really bad,” Mxhasi Sithethi, a regional coordinator for the NUM, said from Rustenburg.Gideon du Plessis, deputy general secretary of the Solidarity trade union which represents skilled workers, said heunderstood AMCU was demanding the NUM close its office at Lonmin.