South Africa's President Jacob Zuma on Friday defended his finance minister from attacks from the ruling party's youth wing and called for action to be taken against ANC members who continue to argue publicly.

His comments, in a letter published on the party's website, are the strongest yet following public spats between members of the alliance linking the African National Congress, trade unions and communist party.

Zuma said criticism of Finance Minister Pravin Gordhan by the ANC Youth League was unacceptable.

"The ANC Youth League issued a statement attacking the Minister of Finance, Comrade Pravin Gordhan, referring to him as an unelected leader. Comrade Gordhan is one of the key and most senior leaders of the ANC and has come a long way," he said.

"If you attack a minister you are also attacking the president, as you are questioning his judgement in appointing that minister ... this behaviour cannot be allowed to continue."

The youth league, an increasingly vocal and significant political force within the ANC, last week accused Gordhan of not following party policy and of ignoring the plight of the young.

The move was just one of several attacks against other party or alliance members, with the league's President Julius Malema also battling the communist party.

The outspoken Malema has unnerved investors with his calls, first made last year, for mines to be nationalised, and targeting Gordhan had threatened to add to uncertainty.

Gordhan succeeded Trevor Manuel in the post when Zuma announced his cabinet in May last year and has been well-received by investors and markets.

Malema is under fire in the media for a lavish lifestyle while claiming to speak for the poor, and was this week found guilty of hate speech for comments made about a person who had accused Zuma of rape.

Labour federation COSATU urged him to be disciplined in a statement earlier this week that also defended Gordhan.

COSATU and the Youth League were important backers of Zuma in his campaign to lead the ANC and the country, but relations have since soured into messy public slanging matches.

Zuma said the fighting must end, reiterating a call from the ANC after its National Executive Committee meeting last weekend.

"This culture of publicly attacking each other will become entrenched if we do not act against it. We will create an image of an organisation and country dogged by tension and infighting," he said in Friday's letter.

"Unless we take decisive action against those who continue to undermine what the NEC has agreed upon, there is simply no reason why we are here. Unless we act upon ill discipline as an organisation, we cannot be trusted to be custodians of the history and traditions of our movement."

Reuters