ANC secretary-general Gwede Mantashe has compared the Congress of South African Trade Unions' (Cosatu's) largest affiliate, the National Union of Metalworkers of South Africa (Numsa) to a person suffering from a lifestyle-related disease, Sowetan reported on Wednesday.

"Sometimes you have a chronic disease that is lifestyle related, [and] instead of behaving properly and doing the right thing, you blame witches," Mantashe was quoted as saying.

On Monday, Numsa said it would forge ahead with the launch of its own political party, the United Front.

The union, which has been at loggerheads with Cosatu, has withdrawn its support for the African National Congress (ANC), saying they no longer represented workers' interests.

Mantashe said the ANC could not impose its views on Cosatu, which bore the onus of working for unity.

This was after Numsa rejected as a "farce" an ANC task team's efforts at mediating Cosatu's internal tensions.

Cosatu said on Friday discussions about Numsa's future in the trade union federation would continue when the special central executive committee meeting, which adjourned last week, reconvened on November 7.