One of the reasons for the Marikana tragedy was the "toxic relationship" between the National Union of Mineworkers (NUM) and the Association of Mineworkers and Construction Union (Amcu), counsel for platinum miner Lonmin Schalk Burger SC said on Thursday.

Mr Burger began his cross-examination of Amcu president Joseph Mathunjwa on Thursday afternoon at the commission of inquiry trying to establish what led to the August 16 standoff between strikers and police, which resulted in the deaths of 34 people.

Mr Mathunjwa had blamed Lonmin management for the events, but Mr Burger suggested that one of the main reasons was the relationship between the two unions. Mr Mathunjwa agreed that the rivalry had contributed to the situation getting out of hand.

He recalled that the NUM had accused Amcu of killing two security officers and had claimed that all the unrest was a ploy by Amcu to unseat it, Mr Mathunjwa said. He further recalled that the NUM had said Amcu had promised workers wages of R12,500 per month.

But Mr Mathunjwa denied Amcu had played any part in fanning the rivalry, although he admitted saying the NUM oppressed workers.

When he spoke of "rent-a-black " while addressing the striking workers on the morning of August 16, he was referring to "the employer" and not the NUM.

"Africa’s economy is in white hands, who arrived here by boats," Mr Mathunjwa said at the time. "They are the ones who control our lives even today. On top of that, what they do is, they take our brothers and give them top positions. That is called rent-a-black in English."

When commission chairman Judge Ian Farlam wanted to know who the rented blacks were, Mr Mathunjwa said he was referring to Lonmin’s black executives, but did not have any particular name in mind. Mr Burger said the Amcu president had made the statement on the morning of the "most inflammatory situation".

Mr Burger further referred to a media statement Mr Mathunjwa issued on August 14 in which he referred to "sinister forces" and "dirty tricks" at the Marikana mine and to an NUM campaign to reclaim Lonmin. On Thursday, Mr Mathunjwa said he did not know who the sinister forces were and that he had even written to management, asking that the matter be investigated.

The "dirty tricks" he spoke of related to the platinum industry bosses who were refusing to accord Amcu organisational rights, which unions with smaller numbers of members had. Mr Burger insisted that because of the toxic relationship between the two unions, Lonmin had "no room" to negotiate with the striking workers outside of the "established structures".

The cross-examination of Mr Mathunjwa continues on Friday.