Lonmin chief executive Ben Magara. Photo: Simphiwe Mbokazi.

Johannesburg - Platinum producer Lonmin has declared force majeure with some suppliers after its miners went on strike more than 10 weeks ago, Chief Executive Ben Magara said on Thursday.

Magara told a media briefing in Johannesburg that the firm had not gone to the open market to buy platinum to supply customers and would only do so as a last resort.

Lonmin's announcement follows similar moves by rivals Impala Platinum and Anglo American Platinum as the prolonged job boycott takes its toll on the world's biggest producers of the precious metal.

Magara also said a survey conducted via cellphone messages showed that most striking workers at Lonmin wanted to return to work. A spokeswoman said the company had about 20,000 mobile phone numbers for its workers, which it had used for the survey.

The Johannesburg-listed shares of Lonmin were up 0.5 percent at 52.36 rand at 0744 GMT.