Former South African Defence Minister Mosiuoa Lekota threatened on Wednesday to split the ruling ANC and form a new party following last month's overthrow of former President Thabo Mbeki.

His threat was the latest move in the worst political crisis since the end of apartheid, unleashed by the ousting of Mbeki at the climax of a power struggle with ANC boss Jacob Zuma.

"It seems that we are serving today divorce papers," Lekota told a news conference after complaining about what he called undemocratic tendencies in the African National Congress, which he said had betrayed its own principles.

The ANC dismissed Lekota's move, calling it a "machination."

"We will definitely not be deterred by the formation of any new political parties," spokeswoman Jessie Duarte said.

But ANC treasurer Mathews Phosa was conciliatory.

"We don't believe the marriage has irretrievably broken down," he said, adding that the party would talk to Lekota "until we get tired of talking."

Lekota did not announce a new grouping as had been predicted although he said the dominant ruling party was near a split.

He called for a congress of forces opposed to the ANC's current policies and direction within four weeks but said he had not spoken to opposition parties.

Investors worried about leftist push

Flanked by another ANC dissident, former Deputy Defence Minister Mluleki George, he said: "Logically it seems that this is the end of it."

Duarte said Lekota had intended to announce a party but something went wrong.

Investors are worried that Zuma, strongly backed by the Communist Party and trade unions, could push South African economic policies to the left if he becomes president after elections next year, as is expected.

Analysts, however, said Lekota's announcement had not affected markets preoccupied by global financial turmoil.

It was not clear how much support Lekota, a former ANC chairman, had, although he said hundreds of local party supporters had resigned and regional and provincial ANC branches were contemplating leaving.

Most analysts played down the impact of any breakaway party unless it was joined by ANC heavyweights including Mbeki. They said the party leadership might welcome the departure of dissidents to restore unity.

Other Mbeki loyalists have remained in the background since his overthrow. Several have denied they will leave the party.

Mbeki was forced out last month and replaced by Kgalema Motlanthe after a judge accused him of meddling in a graft case against Zuma. Motlanthe is expected to step down after elections expected around April 2009.

Lekota complained about tribalism in the ANC and said the leadership had failed to crackdown on supporters singing songs calling for violence. It had also attacked judges as "counter revolutionary" because of judgements unfavourable to Zuma.

Zuma, a sharp contrast to the austere and aloof Mbeki, ousted him as ANC leader last December.

The South African Communist Party, one of Zuma's leftist backers within the ruling alliance, branded Lekota as a rightwinger.

"Finally the beast is in the open," it said.

But the main opposition Democratic Alliance party welcomed Lekota's statement. "The disintegration of the ANC has begun, heralding an exciting new era in South Africa," it said.

With files from Reuters